verity: remove write callback from user-space

Remove the write callback abstraction as it is no longer needed.

BUG=chromium-os:19952
TEST=Ran unit tests from dm-verity.git.
     Ran platform_DMVerityCorruption and platform_DMVerityBitCorruption.
TESTED_ON=Alex

Change-Id: I111c1a5d6a21b1da594a24c94c36af71fca2f816
Reviewed-on: http://gerrit.chromium.org/gerrit/7102
Reviewed-by: Mandeep Singh Baines <msb@chromium.org>
Tested-by: Mandeep Singh Baines <msb@chromium.org>
5 files changed