Remove purging of GPU resources based on flush counts.

We've had a better time-based mechanism available for a long time.

Change-Id: I130ab79dc0e8161a6817eb53b83e0988546dfa71
Reviewed-on: https://skia-review.googlesource.com/152668
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
6 files changed