block: move more syncing and invalidation to delete_partition

Move the calls to fsync_bdev and __invalidate_device from del_gendisk to
delete_partition.  For the other two callers that check that there are
no openers for the delete partitions(s) the callouts are a no-op as no
file system can be mounted, but this keeps all the cleanup in one
place.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20210406062303.811835-4-hch@lst.de


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