Cleaning up the compute_engine_scripts since we no longer have masters/slaves in skia-buildbots.

This CL aggressively deletes everything from the compute_engine_scripts/buildbots directory. We can always bring things back later if required.
The empty perfserver directory is also deleted.

BUG=skia:2958

Review URL: https://codereview.chromium.org/658343004
Remove buildbot/ and repo-serving/ from the redirector since the GCE masters no longer exist

BUG=skia:2958

Review URL: https://codereview.chromium.org/663843002
Open the Tree status webapp in a new tab when clicked from the buildbot console

This is live: http://chromegw.corp.google.com/i/client.skia.internal/console

BUG=skia:3011

Review URL: https://codereview.chromium.org/660323002