Remove old non-compliant Ctrl+Alt+L shortcut that interferes with apps

KScreenLocker lets the user lock the screen with the Meta+L and
Ctrl+Alt+L shortcuts by default. This latter shortcut has been reported
by users to conflict with the Ctrl+Alt+L shortcut in at least one
user-facing app. System components shouldn't break apps by masking
their shortcuts.

This commit removes the Ctrl+Alt+L shortcut, leaving only Meta+L. This
un-breaks userspace apps using that shortcut.

BUG: 454397
FIXED-IN: 5.25


(cherry picked from commit 0ce96496)