Drop support for OSMesa in test tools and remove build bot

Change-Id: Ic85ee05fe292a36a053ca7a20ccce24a4da4fae2
Reviewed-on: https://skia-review.googlesource.com/70026
Reviewed-by: Joe Gregorio <jcgregorio@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
21 files changed