No longer skip CVR authentication in tests where possible

[arsalansufi]

A search for SKIP_CAST_VOTE_RECORDS_AUTHENTICATION should bring up places where we skip CVR authentication in tests. The CVR fixtures now include signature files, so CVR authentication in tests is now possible.

The one gotcha is tests in which we intentionally modify the export (via modifyCastVoteRecordExport for example). We could have modifyCastVoteRecordExport export an updated signature file.

We may still want to skip CVR auth in some tests for speed. And we should still keep the feature flag around for development.