Revert "Add support for semaphores to be inserted on GrContext flush"

This reverts commit cd1416efbc7af6f115dbaa09dce48e075d1d96ca.

Reason for revert: speculative, to try to fix roll see gpu_tests.pixel_integration_test.PixelIntegrationTest.Pixel_GpuRasterization_ConcavePaths

Original change's description:
> Add support for semaphores to be inserted on GrContext flush
> 
> This also moves the logic of inserting semaphores down into GrDrawingManager
> and finishFlush on GrGpu. With it being on finishFlush, there should be no
> issues when the DrawingManager starts respecting the proxy passed in assuming
> it always calls finishFlush at the end (which it should).
> 
> Bug: skia:
> Change-Id: I925c2a289dcbbb9159b9120878af1d34f21a2dc7
> Reviewed-on: https://skia-review.googlesource.com/25641
> Reviewed-by: Brian Salomon <bsalomon@google.com>
> Commit-Queue: Greg Daniel <egdaniel@google.com>

TBR=egdaniel@google.com,bsalomon@google.com,robertphillips@google.com

Change-Id: I9c5b9cf8c060193e1861dbb8f0c10fb11dfb5249
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: skia:
Reviewed-on: https://skia-review.googlesource.com/25980
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Reed <reed@google.com>
25 files changed