GitLab

Use Mac-11.0 only. Remove Mac-10.16 swarming dimension which does not
exist anymore.

Bug: 1156252
Change-Id: Ie8e146cfa6f7e3d6e78756d34e1d661e7b1c8564
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2577759Reviewed-by: Garrett Beaty <gbeaty@chromium.org>
Commit-Queue: Anjali Doneria <adoneria@google.com>
Cr-Commit-Position: refs/heads/master@{#834372}