event_notifier: cleanups around event_notifier_set_handler

Remove the useless is_external argument.  Since the iohandler
AioContext is never used for block devices, aio_disable_external
is never called on it.  This lets us remove stubs/iohandler.c.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

iohandler.c

@@ -66,6 +66,14 @@ void qemu_set_fd_handler(int fd,
                        fd_read, fd_write, NULL, opaque);
 }
 
+void event_notifier_set_handler(EventNotifier *e,
+                                EventNotifierHandler *handler)
+{
+    iohandler_init();
+    aio_set_event_notifier(iohandler_ctx, e, false,
+                           handler, NULL);
+}
+
 /* reaping of zombies.  right now we're not passing the status to
    anyone, but it would be possible to add a callback.  */
 #ifndef _WIN32