MBS-7668: add a stat for the total number of MBIDs we know about
Create a delete method for series.
Merge branch 'mbid-count-stat'

* mbid-count-stat:
  MBS-7668: add a stat for the total number of MBIDs we know about
Merge branch 'series-deletion-fix'

* series-deletion-fix:
  Create a delete method for series.
Whoops, missing semicolon.
Use delete_returning_gids in series deletion code, since that's how inserts to series_deletion happen.