block: disable the elevator int del_gendisk

In the Linux kernel, the following vulnerability has been resolved:

block: disable the elevator int del_gendisk

The elevator is only used for file system requests, which are stopped in

del_gendisk. Move disabling the elevator and freeing the scheduler tags

to the end of del_gendisk instead of doing that work in disk_release and

blk_cleanup_queue to avoid a use after free on q->tag_set from

disk_release as the tag_set might not be alive at that point.

Move the blk_qos_exit call as well, as it just depends on the elevator

exit and would be the only reason to keep the not exactly cheap queue

freeze in disk_release.