remove dead code in bitmapcache

BUG=skia:

Change-Id: If17511179851ac192758f9d96092ff6dd7c60888
Reviewed-on: https://skia-review.googlesource.com/10055
Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Mike Reed <reed@google.com>
3 files changed