Remove GrBackendObject and all related functions from Skia.

Bug: skia:
Change-Id: I59434b7477c0bc26fd982bd81eb97ab94bbba073
Reviewed-on: https://skia-review.googlesource.com/125822
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Greg Daniel <egdaniel@google.com>
31 files changed