Remove fIntendedType from GrMtlBuffer. Add accessor to base class

Fixes unused member warning-as-error.

Change-Id: I9468a1b1cb106eeb7818afe87f5cda7eb75910de
Reviewed-on: https://skia-review.googlesource.com/c/189497
Commit-Queue: Brian Salomon <bsalomon@google.com>
Commit-Queue: Greg Daniel <egdaniel@google.com>
Auto-Submit: Brian Salomon <bsalomon@google.com>
Reviewed-by: Greg Daniel <egdaniel@google.com>
3 files changed