qemu-nbd: remove unnecessary qemu_notify_event()

This was needed when qemu-nbd was using qemu_set_fd_handler2.  It is
not needed anymore now that nbd_update_server_fd_handler is called
whenever nbd_can_accept() can change from false to true.
nbd_update_server_fd_handler will call qemu_set_fd_handler(),
which will call qemu_notify_event().

Reviewed-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

qemu-nbd.c

@@ -362,7 +362,6 @@ static void nbd_client_closed(NBDClient *client)
         state = TERMINATE;
     }
     nbd_update_server_fd_handler(server_fd);
-    qemu_notify_event();
     nbd_client_put(client);
 }