Remove split screen focus change shortcuts

Removing the focus change shortcuts for split screen due to lack of other focus change shortcuts that allow navigating across SysUI surfaces and the current shortcut classes with A11y shortcut requirement.

UX is working on a family of shortcuts for changing focus across Sys UI surfaces (taskbar, status bar, etc) and will include shortcuts for split screen focus changes too. So, just removing the shortcut triggers and keeping the infra to easily add support for these shortcut in future releases.

Bug: 384514582
Test: atest KeyGestureControllerTests
Test: atest WmTests
Flag: EXEMPT bugfix
Change-Id: Ifef0524b037d1de3041cd4d5d4403c1e48d960ad