Remove unused GrSignalSemaphoreOp and forced flushed on semaphore insertion.

Bug: skia:
Change-Id: Iad0e6468552606d7528aaf0307948fe84f85a0d8
Reviewed-on: https://skia-review.googlesource.com/c/175256
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
Commit-Queue: Greg Daniel <egdaniel@google.com>
10 files changed