Remove some more MoltenVK support

Change-Id: I511f15f056e15beddeaaf203414a1519569bfbe4
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/248815
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Jim Van Verth <jvanverth@google.com>
2 files changed