Renamed generated_feature_methods to generated_association_methods.
Remove private API test
Merge pull request #12390 from kennyj/rename_to_association_methods

Renamed generated_feature_methods to generated_association_methods.

Conflicts:
	activerecord/lib/active_record/associations/builder/association.rb
	activerecord/lib/active_record/associations/builder/singular_association.rb
	activerecord/test/cases/base_test.rb