Update taskbar to add extra hotseat items instead of recent apps

Removes recents-related code including the divider between it and
hotseat.

Test: manually on device

Fixes: 184366189
Bug: 184789479
Bug: 171917176
Change-Id: I7776c98659ded70f53a49befddcd23c8353c6440

quickstep/src/com/android/launcher3/BaseQuickstepLauncher.java

@@ -108,6 +108,7 @@ public abstract class BaseQuickstepLauncher extends Launcher
         SysUINavigationMode.INSTANCE.get(this).removeModeChangeListener(this);
         if (mTaskbarController != null) {
             mTaskbarController.cleanup();
+            mTaskbarController = null;
         }
 
         super.onDestroy();