src/queue: kill bogus ktail_next == head check
src/queue: kill bogus ktail_next == head check

This really wants to be a "will we over-fill the ring?" kind of
check, but the sqe_head/sqe_tail should not be that far apart. If they
are, that's a bug elsewhere. So just kill the check.

Signed-off-by: Jens Axboe <cd8c6775e60d6f67a6984377324e5290df3d5358@kernel.dk>

axboe/liburing,axboe/liburing,axboe/liburing