Merge pull request #26451 from kamipo/remove_target_uniq_size

Remove unnecessary `target.uniq.size` in `CollectionAssociation#size`

activerecord/lib/active_record/associations/collection_association.rb

@@ -219,11 +219,7 @@ def destroy(*records)
       # +count_records+, which is a method descendants have to provide.
       def size
         if !find_target? || loaded?
-          if association_scope.distinct_value
-            target.uniq.size
-          else
-            target.size
-          end
+          target.size
         elsif !association_scope.group_values.empty?
           load_target.size
         elsif !association_scope.distinct_value && target.is_a?(Array)