The split screen app shortcut is not intended to work in Desktop Mode.
This change removes it from Taskbar and all apps in this mode to avoid
a crash.
Fix: 346333758
Test: Launch the app menu for different apps in Desktop mode and in
normal mode. Check that the split option only shows up in normal mode.
Flag: EXEMPT bugfix
Change-Id: I6e2535b41a490ad3eb5c0ebd924c49eaf5028669