Remove deprecated discard method and GrCaps support

Change-Id: I231949c90342a44e9c0b6030818139d3164819da
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/226837
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Jim Van Verth <jvanverth@google.com>
11 files changed