Revert "Dupping a CollectionProxy should dup the load_target"

I incorrectly changed behavior of `dup`. Reading the original issue I
thought that `dup` should retain the original contents of the record
and it's associations but it is in fact supposed to be a copy as if a
record had been reinitialized.

This reverts commit ca8c21df.

activerecord/lib/active_record/associations/collection_proxy.rb

@@ -33,10 +33,6 @@ def initialize(klass, association) #:nodoc:
         super klass, klass.arel_table, klass.predicate_builder
       end
 
-      def initialize_dup(other) # :nodoc:
-        @association = @association.deep_dup
-      end
-
       def target
         @association.target
       end

activerecord/test/cases/associations/has_many_associations_test.rb

@@ -2107,14 +2107,6 @@ def test_to_a_should_dup_target
     assert_not_equal target.object_id, ary.object_id
   end
 
-  def test_dup_should_dup_load_target
-    original = topics(:first).replies
-    dupped = topics(:first).replies.dup
-
-    assert_not_equal original.object_id, dupped.object_id
-    assert_not_equal original.load_target.object_id, dupped.load_target.object_id
-  end
-
   def test_merging_with_custom_attribute_writer
     bulb = Bulb.new(color: "red")
     assert_equal "RED!", bulb.color