Remove a legacy mode assertions for the scene container flag

While the CL that added this assertion was in review, A CL merged that
added a call to this.

Bug: 348013571
Test: manual
Flag: com.android.systemui.scene_container
Change-Id: I6c57d9d4a4430790da21d5e9f332d38cf6360312
diff --git a/packages/SystemUI/src/com/android/systemui/statusbar/notification/stack/NotificationStackScrollLayout.java b/packages/SystemUI/src/com/android/systemui/statusbar/notification/stack/NotificationStackScrollLayout.java
index 132d0f0..1789ad6 100644
--- a/packages/SystemUI/src/com/android/systemui/statusbar/notification/stack/NotificationStackScrollLayout.java
+++ b/packages/SystemUI/src/com/android/systemui/statusbar/notification/stack/NotificationStackScrollLayout.java
@@ -6462,7 +6462,6 @@
     };
 
     public HeadsUpTouchHelper.Callback getHeadsUpCallback() {
-        SceneContainerFlag.assertInLegacyMode();
         return mHeadsUpCallback;
     }