[metrics] Remove google3-autoroll metrics source
[metrics] Remove google3-autoroll metrics source

We no longer run a backend for the Google3 roller, so there's no need to
query it for metrics.

Bug: skia:8206
Change-Id: I6b2e1f82f8c672b11a0f00d0bd105933a10f33a9
Reviewed-on: https://skia-review.googlesource.com/148903
Reviewed-by: Ravi Mistry <9fa2e7438b8cb730f96b74865492597170561628@google.com>
Reviewed-by: Ben Wagner <3ef7217be91069877d94f7907ce5479000772cd3@google.com>
Commit-Queue: Eric Boren <0e499112533c8544f0505ea0d08394fb5ad7d8fa@google.com>

google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot