iomap: remove iomap_apply

iomap_apply is unused now, so remove it.

Signed-off-by: Christoph Hellwig <hch@lst.de>
[djwong: rebase this patch to preserve git history of iomap loop control]
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Dave Chinner <dchinner@redhat.com>