ext3: Remove the obsolete broken EXT3_IOC32_WAIT_FOR_READONLY.

There are no user of EXT3_IOC32_WAIT_FOR_READONLY and also it is
broken. No one set the set_ro_timer, no one wake up us and our
state is set to TASK_INTERRUPTIBLE not RUNNING. So remove it.

Cc: Jan Kara <jack@suse.cz>
Signed-off-by: Tao Ma <boyu.mt@taobao.com>
Signed-off-by: Jan Kara <jack@suse.cz>