Remove setting/use of GrPixelConfig in GrBackendTex/RT ctors.

Bug: skia:
Change-Id: I1466668e3502cd1e6e1f6aed4105e0f626d293dd
Reviewed-on: https://skia-review.googlesource.com/138987
Commit-Queue: Greg Daniel <egdaniel@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
16 files changed