Revert "Don't remove the select values to add they back again"

This reverts commit 0785008.

Reason: MySQL tests are broken with this change because STI information
seems to be lost. We will apply a fix only on master for this.

Author: rafaelfranca

activerecord/lib/active_record/relation/finder_methods.rb

@@ -222,7 +222,7 @@ def construct_relation_for_association_calculations
     end
 
     def construct_relation_for_association_find(join_dependency)
-      relation = except(:includes, :eager_load, :preload).select(join_dependency.columns)
+      relation = except(:includes, :eager_load, :preload, :select).select(join_dependency.columns + select_values)
       apply_join_dependency(relation, join_dependency)
     end