The main purpose of this patch is cleanup.
The throtl_adjusted_limit function was removed after
commit bf20ab538c81 ("blk-throttle: remove
CONFIG_BLK_DEV_THROTTLING_LOW"), so the problem of not being
able to scale after setting bps or iops to 1 will not occur.
So revert this commit that bps/iops can be set to 1.