Remove @hide for KEYCODE_ALL_APPS

    - KEYCODE_ALL_APPS which was introduced late in O is now a
      proper & valid keycode in P

Bug: 64935695
Test: Manual: ALL_APPS: adb shell input keyevent 284
Test: also tested with --longpress for these keys

Change-Id: If56c5b87f88e927c52468485b790581fa19ad48b