Make GrVkBackendContext no longer derive from SkRefCnt.

Also moves the helper Create functions to VkTestUtils since no clients
are using them anymore.

Bug: skia:
Change-Id: I7e8e4912e7ef6fb00a7e2a00407aed5e83211799
Reviewed-on: https://skia-review.googlesource.com/135323
Reviewed-by: Jim Van Verth <jvanverth@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Greg Daniel <egdaniel@google.com>
13 files changed