Since the upload ID is part of the primary key, we can avoid using the
RecordLabels table to find matching records. This takes the query
"upload:20170127.22 name:Gzip" from ~0.3s to ~0.04s on our production
database.

Change-Id: Id31624ec1b81f3a7f648c6597392718c56a10edd
Reviewed-on: https://go-review.googlesource.com/37236
Run-TryBot: Quentin Smith <quentin@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>