Oracle TIMESTAMP sql type is associated with Rails DateTime type now

- Refer https://github.com/rsim/oracle-enhanced/pull/845
Remove `set_date_columns` which has been deprecated in Oracle enhanced adapter
 - Refer https://github.com/rsim/oracle-enhanced/pull/869

activerecord/test/cases/migration/column_attributes_test.rb

@@ -156,14 +156,7 @@ module ActiveRecord
           assert_equal String, bob.bio.class
           assert_kind_of Integer, bob.age
           assert_equal Time, bob.birthday.class
-
-          if current_adapter?(:OracleAdapter)
-            # Oracle doesn't differentiate between date/time
-            assert_equal Time, bob.favorite_day.class
-          else
           assert_equal Date, bob.favorite_day.class
-          end
-
           assert_instance_of TrueClass, bob.male?
           assert_kind_of BigDecimal, bob.wealth
         end

activerecord/test/models/topic.rb

@@ -43,12 +43,6 @@ class Topic < ActiveRecord::Base
   before_create  :default_written_on
   before_destroy :destroy_children
 
-  # Explicitly define as :date column so that returned Oracle DATE values would be typecasted to Date and not Time.
-  # Some tests depend on assumption that this attribute will have Date values.
-  if current_adapter?(:OracleEnhancedAdapter)
-    set_date_columns :last_read
-  end
-
   def parent
     Topic.find(parent_id)
   end