Revert "scsi, block: fix duplicate bdi name registration crashes"

Revert "scsi, block: fix duplicate bdi name registration crashes"

This reverts commit 0dba1314d4f81115dce711292ec7981d17231064. It causes
leaking of device numbers for SCSI when SCSI registers multiple gendisks
for one request_queue in succession. It can be easily reproduced using
Omar's script [1] on kernel with CONFIG_DEBUG_TEST_DRIVER_REMOVE.
Furthermore the protection provided by this commit is not needed anymore
as the problem it was fixing got also fixed by commit 165a5e22fafb
"block: Move bdi_unregister() to del_gendisk()".

[1]: http://marc.info/?l=linux-block&m=148554717109098&w=2

Signed-off-by: Jan Kara <[email protected]>
Acked-by: Dan Williams <[email protected]>
Tested-by: Omar Sandoval <[email protected]>
Signed-off-by: Jens Axboe <[email protected]>