loop: remove loop.h

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2083917



commit 754d9679
Author: Christoph Hellwig <hch@lst.de>
Date:   Tue Apr 19 08:33:00 2022 +0200

    loop: remove loop.h

    Merge loop.h into loop.c as all the content is only used there.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
    Link: https://lore.kernel.org/r/20220419063303.583106-2-hch@lst.de


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

Signed-off-by: Ming Lei <ming.lei@redhat.com>