io_uring: remove extra in_idle wake up

io_dismantle_req() is always followed by io_put_task(), which already do
proper in_idle wake ups, so we can skip waking the owner task in
io_dismantle_req(). The rules are simpler now, do io_put_task() shortly
after ending a request, and it will be fine.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>