nvme: remove the GENHD_FL_UP check in nvme_ns_remove

Early probe failure never reaches nvme_ns_remove, so GENHD_FL_UP must
be set at this point.  Remove the check.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20210809064028.1198327-4-hch@lst.de


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