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.