Remove GrBackendTextureDesc

Change-Id: I2b123d1782400e97ab2ce2f11e3e3d325a13e6c8
Reviewed-on: https://skia-review.googlesource.com/24748
Commit-Queue: Brian Salomon <bsalomon@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
30 files changed