ao_pipewire: don't access core after disconnect

pw_core_disconnect frees the core, so accessing it afterward to
destroy the context is not allowed.

Instead, just destroy the context, the first thing it does is disconnect
all cores for us.

audio/out/ao_pipewire.c

@@ -245,7 +245,6 @@ static void uninit(struct ao *ao)
         pw_stream_destroy(p->stream);
     p->stream = NULL;
     if (p->core) {
-        pw_core_disconnect(p->core);
         pw_context_destroy(pw_core_get_context(p->core));
     }
     p->core = NULL;