Revert "[1/2] Buttons: Switch to last app"

This reverts commit 926b30737d9b562ca8e73e51c2f54835d7342ca1.

Change-Id: I4676914efb381a543b8c977fdabb2a3d000fe5fd
frameworks: allow last app action to be assigned to hardware keys

Also fix multi-user handling for 'switch to last app' and 'kill
foreground app' actions.

Change-Id: I1fb586d19b1198e6888b0f11e0a2813acf0bcd5b
Signed-off-by: Roman Birg <roman@cyngn.com>
Signed-off-by: Danny Baumann <dannybaumann@web.de>