delete some votes to avoid duplicates

this adds a test where bill_id-tied votes are deleted on import
of new votes so that dupes aren't created.  this breaks detection
of updates and is overly aggressive, so right now part of
a vote test is commented out, next commit will break tests by
uncommenting that portion of the code
uncomment failing portion of vote import test
delete the votes at the end, not during the import
Merge branch 'master' of github.com:opencivicdata/pupa