Proto-proof the identifiers_test
Proto-proof the identifiers_test

Summary:
Some proto generators add extra fields so nameless struct
instantiations break. This change removes these instantiations from
identifiers_test.

Test Plan: Tests still pass

Reviewers: zarko, schroederc

Reviewed By: schroederc

Subscribers: #core_team

Differential Revision: https://phabricator-dot-kythe-repo.appspot.com/D1929

benjyw/kythe,bzz/kythe,benjyw/kythe,benjyw/kythe,benjyw/kythe,kythe/kythe,kythe/kythe,bzz/kythe,bzz/kythe,kythe/kythe,kythe/kythe,kythe/kythe,benjyw/kythe,bzz/kythe,kythe/kythe,bzz/kythe,bzz/kythe,bzz/kythe,bzz/kythe,bzz/kythe,kythe/kythe,benjyw/kythe,benjyw/kythe,benjyw/kythe,kythe/kythe,benjyw/kythe,benjyw/kythe,benjyw/kythe,benjyw/kythe,bzz/kythe,kythe/kythe,bzz/kythe,kythe/kythe,bzz/kythe,kythe/kythe