loop: don't set QUEUE_FLAG_NOMERGES

loop: don't set QUEUE_FLAG_NOMERGES

QUEUE_FLAG_NOMERGES isn't really a driver interface, but a user tunable.
There also isn't any good reason to set it in the loop driver.

The original commit adding it (5b5e20f421c0b6d "block: loop: set
QUEUE_FLAG_NOMERGES for request queue of loop") claims that "It doesn't
make sense to enable merge because the I/O submitted to backing file is
handled page by page."  which of course isn't true for multi-page bvec
now, and it never has been for direct I/O, for which commit 40326d8a33d
("block/loop: allow request merge for directio mode") alredy disabled
the nomerges flag.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Link: https://lore.kernel.org/r/20240627124926.512662-2-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>