remove mac bots, friend of https://codereview.chromium.org/1659273003
remove mac bots, friend of https://codereview.chromium.org/1659273003

presubmit spewed tons of unrelated Go errors, so I've ignored it.

BUG=skia:

Review URL: https://codereview.chromium.org/1663883004

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