Remove GrProxyPendingIO

Change-Id: I9cf40f0518673206c6304e3f386dd75c9a44f269
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/235865
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
6 files changed