fix(client): remove unnecessary wl_output_roundtrip

At this point we're not awaiting any protocol events and flushing
wayland queue makes little sense. As #1019 shows, it may be even harmful
as an extra roundtrip could process wl_output disappearance and delete
output object right from under our code.

src/client.cpp

@@ -124,7 +124,6 @@ void waybar::Client::handleOutputDone(void *data, struct zxdg_output_v1 * /*xdg_
 
     auto configs = client->getOutputConfigs(output);
     if (!configs.empty()) {
-      wl_display_roundtrip(client->wl_display);
       for (const auto &config : configs) {
         client->bars.emplace_back(std::make_unique<Bar>(&output, config));
       }