Removing back-button alpha animation code

Back button is only animation in 2-button UI which is not supported anymore

Bug: 246006580
Test: Presubmit
Change-Id: I7385b07272e44c1f9f0488c158e1b4ee67060120

src/com/android/launcher3/AbstractFloatingView.java

@@ -109,10 +109,6 @@ public abstract class AbstractFloatingView extends LinearLayout implements Touch
             | TYPE_ALL_APPS_EDU | TYPE_ICON_SURFACE | TYPE_WIDGETS_EDUCATION_DIALOG
             | TYPE_TASKBAR_EDUCATION_DIALOG | TYPE_TASKBAR_ALL_APPS | TYPE_OPTIONS_POPUP_DIALOG;
 
-    // Usually we show the back button when a floating view is open. Instead, hide for these types.
-    public static final int TYPE_HIDE_BACK_BUTTON = TYPE_ON_BOARD_POPUP | TYPE_DISCOVERY_BOUNCE
-            | TYPE_SNACKBAR | TYPE_WIDGET_RESIZE_FRAME | TYPE_LISTENER;
-
     public static final int TYPE_ACCESSIBLE = TYPE_ALL & ~TYPE_DISCOVERY_BOUNCE & ~TYPE_LISTENER
             & ~TYPE_ALL_APPS_EDU;