verity: remove verify_mode

verity: remove verify_mode

We don't really use verify_mode any more. We used to use it when
dm_bht_compute called verify_path but that is no longer the case.

I'm sending this patch now because it makes the LOCALLY_VERIFIED state
patch I'm working on a little cleaner. So this is really work
leading up to that.

BUG=9752
TEST=Ran platform_DMVerityCorruption on H/W.

Signed-off-by: Mandeep Singh Baines <msb@chromium.org>;
kernel.git Review URL: http://codereview.chromium.org/6659037

TBRing because code has already been LGTMed and commited to kernel.git.

Change-Id: I09b2e9b7caeb7020c14fb7d2366e463afee9b515

TBR=wad@chromium.org,taysom@chromium.org,ups@chromium.org

Committed: http://chrome-svn/viewvc/chromeos?view=rev&revision=2d71629