clean up SkBitmapProcState::platformProcs()

Cq-Include-Trybots: luci.chromium.try:linux-blink-rel
Change-Id: Ief41c0442ce37ba0350d070a66a103095c07083c
Reviewed-on: https://skia-review.googlesource.com/c/172420
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
9 files changed