Fix new RGC subscription IDs

I stripped the R G prefix around 8/23, causing failure to recur.  This
patch rolls back that part of the change, since 3+ queries rely on the
prefix.

Backfill might be annoyingly heuristic, cos there is no gateway field to
identify the GC subscriptions, if there has never been a successful
contribution.

Change-Id: Id9f611be3cac102c838ba60eea2c0e6e78443d44
Merge remote-tracking branch 'origin/master' into HEAD

Change-Id: I8d4b925d86a18252eb161a73095d8053e3ec5149