Remove sample locations usage from GL backend

Bug: skia:8921

Change-Id: If9e65a78f9e1fddb5c5ad5afa5612294935122e5
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/386837
Reviewed-by: Chris Dalton <csmartdalton@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
26 files changed