Make SkGr.h private and remove unused functions

BUG=skia:

Change-Id: I6699d00c5412ed9d9bf14b032a08b06b1c766bce
Reviewed-on: https://skia-review.googlesource.com/9398
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
42 files changed