Don't modify fv old-style bitmaps

* Just make new "bmp" files as necessary

BUG=chrome-os-partner:2558
TEST=runs as expected

Change-Id: I3046630ea3e3f0a40429bb63a986c6044b83c6a6

Review URL: http://codereview.chromium.org/6623008
(cherry picked from commit d221f223bdf97912101747d029403053dadf6da5)

Review URL: http://codereview.chromium.org/6686025