Remove unused Arel::Attributes classes

I missed it in #36493, those classes should also no longer be used since
https://github.com/rails/arel/pull/196.

activerecord/lib/arel/attributes/attribute.rb

@@ -27,14 +27,6 @@ module Arel # :nodoc: all
         relation.able_to_type_cast?
       end
     end
-
-    class String    < Attribute; end
-    class Time      < Attribute; end
-    class Boolean   < Attribute; end
-    class Decimal   < Attribute; end
-    class Float     < Attribute; end
-    class Integer   < Attribute; end
-    class Undefined < Attribute; end
   end
 
   Attribute = Attributes::Attribute

activerecord/lib/arel/visitors/dot.rb

@@ -167,16 +167,10 @@ module Arel # :nodoc: all
           visit_edge o, "attribute"
         end
 
-        def visit_Arel_Attribute(o)
+        def visit_Arel_Attributes_Attribute(o)
           visit_edge o, "relation"
           visit_edge o, "name"
         end
-        alias :visit_Arel_Attributes_Integer :visit_Arel_Attribute
-        alias :visit_Arel_Attributes_Float :visit_Arel_Attribute
-        alias :visit_Arel_Attributes_String :visit_Arel_Attribute
-        alias :visit_Arel_Attributes_Time :visit_Arel_Attribute
-        alias :visit_Arel_Attributes_Boolean :visit_Arel_Attribute
-        alias :visit_Arel_Attributes_Attribute :visit_Arel_Attribute
 
         def nary(o)
           o.children.each_with_index do |x, i|

activerecord/test/cases/arel/visitors/to_sql_test.rb

@@ -322,11 +322,6 @@ module Arel
         }
       end
 
-      it "should visit visit_Arel_Attributes_Time" do
-        attr = Attributes::Time.new(@attr.relation, @attr.name)
-        compile attr
-      end
-
       it "should visit_TrueClass" do
         test = Table.new(:users)[:bool].eq(true)
         _(compile(test)).must_be_like %{ "users"."bool" = 't' }
@@ -445,22 +440,22 @@ module Arel
 
       describe "Nodes::InfixOperation" do
         it "should handle Multiplication" do
-          node = Arel::Attributes::Decimal.new(Table.new(:products), :price) * Arel::Attributes::Decimal.new(Table.new(:currency_rates), :rate)
+          node = Arel::Attribute.new(Table.new(:products), :price) * Arel::Attribute.new(Table.new(:currency_rates), :rate)
           _(compile(node)).must_equal %("products"."price" * "currency_rates"."rate")
         end
 
         it "should handle Division" do
-          node = Arel::Attributes::Decimal.new(Table.new(:products), :price) / 5
+          node = Arel::Attribute.new(Table.new(:products), :price) / 5
           _(compile(node)).must_equal %("products"."price" / 5)
         end
 
         it "should handle Addition" do
-          node = Arel::Attributes::Decimal.new(Table.new(:products), :price) + 6
+          node = Arel::Attribute.new(Table.new(:products), :price) + 6
           _(compile(node)).must_equal %(("products"."price" + 6))
         end
 
         it "should handle Subtraction" do
-          node = Arel::Attributes::Decimal.new(Table.new(:products), :price) - 7
+          node = Arel::Attribute.new(Table.new(:products), :price) - 7
           _(compile(node)).must_equal %(("products"."price" - 7))
         end
 
@@ -483,35 +478,35 @@ module Arel
         end
 
         it "should handle BitwiseAnd" do
-          node = Arel::Attributes::Integer.new(Table.new(:products), :bitmap) & 16
+          node = Arel::Attribute.new(Table.new(:products), :bitmap) & 16
           _(compile(node)).must_equal %(("products"."bitmap" & 16))
         end
 
         it "should handle BitwiseOr" do
-          node = Arel::Attributes::Integer.new(Table.new(:products), :bitmap) | 16
+          node = Arel::Attribute.new(Table.new(:products), :bitmap) | 16
           _(compile(node)).must_equal %(("products"."bitmap" | 16))
         end
 
         it "should handle BitwiseXor" do
-          node = Arel::Attributes::Integer.new(Table.new(:products), :bitmap) ^ 16
+          node = Arel::Attribute.new(Table.new(:products), :bitmap) ^ 16
           _(compile(node)).must_equal %(("products"."bitmap" ^ 16))
         end
 
         it "should handle BitwiseShiftLeft" do
-          node = Arel::Attributes::Integer.new(Table.new(:products), :bitmap) << 4
+          node = Arel::Attribute.new(Table.new(:products), :bitmap) << 4
           _(compile(node)).must_equal %(("products"."bitmap" << 4))
         end
 
         it "should handle BitwiseShiftRight" do
-          node = Arel::Attributes::Integer.new(Table.new(:products), :bitmap) >> 4
+          node = Arel::Attribute.new(Table.new(:products), :bitmap) >> 4
           _(compile(node)).must_equal %(("products"."bitmap" >> 4))
         end
 
         it "should handle arbitrary operators" do
           node = Arel::Nodes::InfixOperation.new(
             "&&",
-            Arel::Attributes::String.new(Table.new(:products), :name),
-            Arel::Attributes::String.new(Table.new(:products), :name)
+            Arel::Attribute.new(Table.new(:products), :name),
+            Arel::Attribute.new(Table.new(:products), :name)
           )
           _(compile(node)).must_equal %("products"."name" && "products"."name")
         end
@@ -519,12 +514,12 @@ module Arel
 
       describe "Nodes::UnaryOperation" do
         it "should handle BitwiseNot" do
-          node = ~ Arel::Attributes::Integer.new(Table.new(:products), :bitmap)
+          node = ~ Arel::Attribute.new(Table.new(:products), :bitmap)
           _(compile(node)).must_equal %( ~ "products"."bitmap")
         end
 
         it "should handle arbitrary operators" do
-          node = Arel::Nodes::UnaryOperation.new("!", Arel::Attributes::String.new(Table.new(:products), :active))
+          node = Arel::Nodes::UnaryOperation.new("!", Arel::Attribute.new(Table.new(:products), :active))
           _(compile(node)).must_equal %( ! "products"."active")
         end
       end