block: remove the anticipatory IO scheduler

block: remove the anticipatory IO scheduler

AS is mostly a subset of CFQ, so there's little point in still
providing this separate IO scheduler. Hopefully at some point we
can get down to one single IO scheduler again, at least this brings
us closer by having only one intelligent IO scheduler.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>