Delete GLBench and subclasses

Bug: skia:6305
Change-Id: I3b2f2a8898f25d3dd0ec47668895dd4d00668575
Reviewed-on: https://skia-review.googlesource.com/82040
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
6 files changed