clean up SkBitmapProcState a bit

  - remove dead code
  - fold some headers back into SkBitmapProcState.cpp
  - misc cleanup

Change-Id: I8706efec086ac9ab5795f59de4a60c8d1bb75a7b
Reviewed-on: https://skia-review.googlesource.com/c/171589
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
6 files changed