main-loop: use GSource to poll AIO file descriptors

This lets us remove the hooks for the main loop in async.c.

Reviewed-by: Anthony Liguori <aliguori@us.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

main-loop.h

@@ -302,6 +302,5 @@ void qemu_iohandler_poll(fd_set *readfds, fd_set *writefds, fd_set *xfds, int rc
 
 QEMUBH *qemu_bh_new(QEMUBHFunc *cb, void *opaque);
 void qemu_bh_schedule_idle(QEMUBH *bh);
-int qemu_bh_poll(void);
 
 #endif