remove vestigle code for lockpixels

Bug: skia:6481
Change-Id: Icfd53981b8588fbea74fca2e3be58bc6f13ef923
Reviewed-on: https://skia-review.googlesource.com/13968
Reviewed-by: Matt Sarett <msarett@google.com>
Commit-Queue: Mike Reed <reed@google.com>
7 files changed