io_uring: remove IOU_F_TWQ_FORCE_NORMAL

Extract a function for non-local task_work_add, and use it directly from
io_move_task_work_from_local(). Now we don't use IOU_F_TWQ_FORCE_NORMAL
and it can be killed.

As a small positive side effect we don't grab task->io_uring in
io_req_normal_work_add anymore, which is not needed for
io_req_local_work_add().

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/2e55571e8ff2927ae3cc12da606d204e2485525b.1687518903.git.asml.silence@gmail.com


Signed-off-by: Jens Axboe <axboe@kernel.dk>