Don't pass useless table_name to ModelMetadata.new

The `model_metadata` is only used if `model_class` is given.

If `model_class` is given, the `table_name` is always
`model_class.table_name`.

activerecord/lib/active_record/fixture_set/model_metadata.rb

@@ -3,9 +3,8 @@
 module ActiveRecord
   class FixtureSet
     class ModelMetadata # :nodoc:
-      def initialize(model_class, table_name)
+      def initialize(model_class)
         @model_class = model_class
-        @table_name  = table_name
       end
 
       def primary_key_name
@@ -23,18 +22,12 @@ module ActiveRecord
 
       def timestamp_column_names
         @timestamp_column_names ||=
-          %w(created_at created_on updated_at updated_on) & column_names
+          %w(created_at created_on updated_at updated_on) & @model_class.column_names
       end
 
       def inheritance_column_name
         @inheritance_column_name ||= @model_class && @model_class.inheritance_column
       end
-
-      private
-
-        def column_names
-          @column_names ||= @model_class.connection.columns(@table_name).collect(&:name)
-        end
     end
   end
 end

activerecord/lib/active_record/fixture_set/table_rows.rb

@@ -58,7 +58,7 @@ module ActiveRecord
       end
 
       def model_metadata
-        @model_metadata ||= ModelMetadata.new(model_class, table_name)
+        @model_metadata ||= ModelMetadata.new(model_class)
       end
 
       def resolve_sti_reflections(row)

activerecord/lib/active_record/fixtures.rb

@@ -629,9 +629,7 @@ module ActiveRecord
 
       @fixtures = read_fixture_files(path)
 
-      @table_name = (model_class.respond_to?(:table_name) ?
-                      model_class.table_name :
-                      self.class.default_fixture_table_name(name, config))
+      @table_name = model_class&.table_name || self.class.default_fixture_table_name(name, config)
     end
 
     def [](x)