block: move the remaining elv.icq handling to the I/O scheduler

After the prepare side has been moved to the only I/O scheduler that
cares, do the same for the cleanup and the NULL initialization.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20211126115817.2087431-9-hch@lst.de


Signed-off-by: Jens Axboe <axboe@kernel.dk>