Revert "scsi: scsi_debug: Address races following module load"

Revert the patch mentioned in the subject since it blocks I/O after module
unload has started while this is a legitimate use case. For e.g.  blktests
test case srp/001 that patch causes a command timeout to be triggered for
the following call stack:

__schedule+0x4c3/0xd20
schedule+0x82/0x110
schedule_timeout+0x122/0x200
io_schedule_timeout+0x7b/0xc0
__wait_for_common+0x2bc/0x380
wait_for_completion_io_timeout+0x1d/0x20
blk_execute_rq+0x1db/0x200
__scsi_execute+0x1fb/0x310
sd_sync_cache+0x155/0x2c0 [sd_mod]
sd_shutdown+0xbb/0x190 [sd_mod]
sd_remove+0x5b/0x80 [sd_mod]
device_remove+0x9a/0xb0
device_release_driver_internal+0x2c5/0x360
device_release_driver+0x12/0x20
bus_remove_device+0x1aa/0x270
device_del+0x2d4/0x640
__scsi_remove_device+0x168/0x1a0
scsi_forget_host+0xa8/0xb0
scsi_remove_host+0x9b/0x150
sdebug_driver_remove+0x3d/0x140 [scsi_debug]
device_remove+0x6f/0xb0
device_release_driver_internal+0x2c5/0x360
device_release_driver+0x12/0x20
bus_remove_device+0x1aa/0x270
device_del+0x2d4/0x640
device_unregister+0x18/0x70
sdebug_do_remove_host+0x138/0x180 [scsi_debug]
scsi_debug_exit+0x45/0xd5 [scsi_debug]
__do_sys_delete_module.constprop.0+0x210/0x320
__x64_sys_delete_module+0x1f/0x30
do_syscall_64+0x35/0x80
entry_SYSCALL_64_after_hwframe+0x44/0xae

Link: https://lore.kernel.org/r/20220409043704.28573-1-bvanassche@acm.org
Fixes: 2aad3cd8 ("scsi: scsi_debug: Address races following module load")
Cc: Douglas Gilbert <dgilbert@interlog.com>
Cc: Yi Zhang <yi.zhang@redhat.com>
Cc: Bob Pearson <rpearsonhpe@gmail.com>
Reported-by: Yi Zhang <yi.zhang@redhat.com>
Tested-by: Yi Zhang <yi.zhang@redhat.com>
Acked-by: Douglas Gilbert <dgilbert@interlog.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>