block: remove outdated AioContext locking comments

block: remove outdated AioContext locking comments

The AioContext lock no longer exists.

There is one noteworthy change:

  - * More specifically, these functions use BDRV_POLL_WHILE(bs), which
  - * requires the caller to be either in the main thread and hold
  - * the BlockdriverState (bs) AioContext lock, or directly in the
  - * home thread that runs the bs AioContext. Calling them from
  - * another thread in another AioContext would cause deadlocks.
  + * More specifically, these functions use BDRV_POLL_WHILE(bs), which requires
  + * the caller to be either in the main thread or directly in the home thread
  + * that runs the bs AioContext. Calling them from another thread in another
  + * AioContext would cause deadlocks.

I am not sure whether deadlocks are still possible. Maybe they have just
moved to the fine-grained locks that have replaced the AioContext. Since
I am not sure if the deadlocks are gone, I have kept the substance
unchanged and just removed mention of the AioContext.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-ID: <20231205182011.1976568-15-stefanha@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>