[CD Taskbar] Remove legacy all apps button (secondary display)

Remove legacy all apps UI from secondary display. This is a quick temporary fix just to remove the legacy all apps button for aesthetic purposes without breaking secondary display launcher. The button will appear invisible. A more robust removal will be done when secondary launcher is eradicated completely.

Bug: 398196983
Test: m
Flag: com.android.window.flags.enable_taskbar_connected_displays
Change-Id: Ic5bc44efd479f7298e346d9d45fbb6f24dfad5d3