Revert "Guard task queue id for fuchsia (flutter#26542)" (flutter#29042)

This reverts commit 60ffab0.

Author: arbreng

shell/common/vsync_waiter.cc

@@ -133,13 +133,8 @@ void VsyncWaiter::FireCallback(fml::TimePoint frame_start_time,
 
     TRACE_FLOW_BEGIN("flutter", kVsyncFlowName, flow_identifier);
 
-    fml::TaskQueueId ui_task_queue_id = fml::_kUnmerged;
-    if (pause_secondary_tasks) {
-      // Guarding `GetTaskQueueId` behind `pause_secondary_tasks` as on Fuchsia
-      // the task runners don't initialize message loop task queues.
-      // Once the migration to embedder API is done, this can be deleted.
-      ui_task_queue_id = task_runners_.GetUITaskRunner()->GetTaskQueueId();
-    }
+    fml::TaskQueueId ui_task_queue_id =
+        task_runners_.GetUITaskRunner()->GetTaskQueueId();
 
     task_runners_.GetUITaskRunner()->PostTask(
         [ui_task_queue_id, callback, flow_identifier, frame_start_time,