Remove all Mac 10.13 and 10.14 jobs.

Bug: b/315554697
Bug: b/330350366
Change-Id: I3cd987fddbf8eac0172e81147b93548612e5041d
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/841636
Commit-Queue: Joe Gregorio <jcgregorio@google.com>
Reviewed-by: Ben Wagner <bungeman@google.com>
Reviewed-by: John Stiles <johnstiles@google.com>
3 files changed