Re-enable support for Metal on iOS 10

Change-Id: I16208249405d61af9ec2b974a1a676296cafba79
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/417001
Commit-Queue: Jim Van Verth <jvanverth@google.com>
Reviewed-by: John Stiles <johnstiles@google.com>
2 files changed