AU: Make delta generator skip bsdiff for libWVDecryptDecode.so.

Currently, bsdiff hangs indefinitely on this file so delta generation doesn't
complete. Note that this is a server side fix intended to be in R12 only with
very limited life time. Fixes in R13/ToT are tracked in crosbug.com/p/3785 and
crosbug.com/15274.

BUG=chromium-os:15308
TEST=tested delta generation on a case that used to fail.

Change-Id: Id4dd525a13113be5fa2ae7f19cf0778ffa6f5b95
Reviewed-on: http://gerrit.chromium.org/gerrit/873
Tested-by: Darin Petkov <petkov@chromium.org>
Reviewed-by: Thieu Le <thieule@chromium.org>
Reviewed-by: Ryan Cairns <rtc@chromium.org>
Tested-by: Scott Zawalski <scottz@google.com>