io_uring: remove extra SQPOLL overflow flush

c1edbf5f ("io_uring: flag SQPOLL busy condition to userspace")
added an extra overflowed CQE flush in the SQPOLL submission path due to
backpressure, which was later removed. Remove the flush and let
io_cqring_wait() / iopoll handle it.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/2a83b0724ca6ca9d16c7d79a51b77c81876b2e39.1712708261.git.asml.silence@gmail.com


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