block: Remove unused callback function *bdrv_aio_pdiscard

block: Remove unused callback function *bdrv_aio_pdiscard

The bytes type in *bdrv_aio_pdiscard should be int64_t rather than int.

There are no drivers implementing the *bdrv_aio_pdiscard() callback,
it appears to be an unused function. Therefore, we'll simply remove it
instead of fixing it.

Additionally, coroutine-based callbacks are preferred. If someone needs
to implement bdrv_aio_pdiscard, a coroutine-based version would be
straightforward to implement.

Signed-off-by: Sunny Zhu <sunnyzhyy@qq.com>
Message-ID: <tencent_7140D2E54157D98CF3D9E64B1A007A1A7906@qq.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>