Revert "io_uring: Add support for napi_busy_poll"

This reverts commit adc8682e

.

There's some discussion on the API not being as good as it can be.
Rather than ship something and be stuck with it forever, let's revert
the NAPI support for now and work on getting something sorted out
for the next kernel release instead.

Link: https://lore.kernel.org/io-uring/b7bbc124-8502-0ee9-d4c8-7c41b4487264@kernel.dk/
Signed-off-by: Jens Axboe <axboe@kernel.dk>