Remove prometheus from Skolo
Remove prometheus from Skolo

Discussed with Joe. We currently aren't getting any data or alerts from
Skolo, so at the moment running prometheus isn't useful. Hooking up
alerts and metrics for the current setup would be somewhat complex, and
the sk8s replacement will be ready Real Soon Now, so for the time being,
we'll remove prometheus.

Change-Id: I64ed20fd4b67991ccdc5714a11cdba0cca71e094
Reviewed-on: https://skia-review.googlesource.com/c/buildbot/+/259824
Commit-Queue: Ben Wagner aka dogben <3ef7217be91069877d94f7907ce5479000772cd3@google.com>
Commit-Queue: Joe Gregorio <b9cf2471ff6d33504cafe8e6f356b732b2cadced@google.com>
Auto-Submit: Ben Wagner aka dogben <3ef7217be91069877d94f7907ce5479000772cd3@google.com>
Reviewed-by: Joe Gregorio <b9cf2471ff6d33504cafe8e6f356b732b2cadced@google.com>

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