Remove browser_tests from Mac10.13 Tests & mac_chromium_rel_ng.

We're experimenting with fixes in ways that may have adverse
consequences on the performance of the suite. Removing it from
the 10.13 bot should insulate the CQ from those consequences.

TBR=rsesek@chromium.org,ellyjones@chromium.org

No-Try: true
Bug: 828031
Change-Id: I3d203688dbe9b037db9fb52614c942ee84ed111f
Reviewed-on: https://chromium-review.googlesource.com/c/1274059
Reviewed-by: John Budorick <jbudorick@chromium.org>
Commit-Queue: John Budorick <jbudorick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#598448}
2 files changed