Provide AllApps item OnLongClickListener through ActivityContext.

This cleans up how alternative AllApps implementations such as Taskbar
and SecondaryDisplay override the default INSTANCE_ALL_APPS listener.
This change will also be helpful for Toast in Taskbar drag-n-drop.

Test: Manual
Bug: 289261756
Flag: n/a
Change-Id: I55eb881bcd1e210852d435a3ea2a6686ce0a9838

src/com/android/launcher3/allapps/ActivityAllAppsContainerView.java

@@ -892,15 +892,6 @@ public class ActivityAllAppsContainerView<T extends Context & ActivityContext>
         container.put(R.id.work_tab_state_id, state);
     }
 
-    /**
-     * Sets the long click listener for icons
-     */
-    public void setOnIconLongClickListener(OnLongClickListener listener) {
-        for (AdapterHolder holder : mAH) {
-            holder.mAdapter.setOnIconLongClickListener(listener);
-        }
-    }
-
     public AllAppsStore getAppsStore() {
         return mAllAppsStore;
     }