remove unnecessary code

it was added in 36129f2
but isn't useful anymore as corresponding tests pass without it

Author: lest

activerecord/lib/active_record/attribute_methods/dirty.rb

@@ -58,8 +58,6 @@ def write_attribute(attr, value)
           @changed_attributes.delete(attr) unless _field_changed?(attr, old, value)
         else
           old = clone_attribute_value(:read_attribute, attr)
-          # Save Time objects as TimeWithZone if time_zone_aware_attributes == true
-          old = old.in_time_zone if clone_with_time_zone_conversion_attribute?(attr, old)
           @changed_attributes[attr] = old if _field_changed?(attr, old, value)
         end
 
@@ -92,10 +90,6 @@ def _field_changed?(attr, old, value)
 
         old != value
       end
-
-      def clone_with_time_zone_conversion_attribute?(attr, old)
-        old.class.name == "Time" && time_zone_aware_attributes && !self.skip_time_zone_conversion_for_attributes.include?(attr.to_sym)
-      end
     end
   end
 end