remove lock tracking in bitmaps -- they are always locked

Bug: skia:6481
Change-Id: I551c9fd5cdf1ea99fc62042d24d638a1021c348d
Reviewed-on: https://skia-review.googlesource.com/13473
Reviewed-by: Matt Sarett <msarett@google.com>
Commit-Queue: Mike Reed <reed@google.com>
2 files changed