KeyEvent: update comment

Change-Id: I1ea491e7e23670bf0ea83392710010b557803178
Don't let apps disable the SIM PIN entry screen.

As the user (who controls the app behaviour after all) likely doesn't
see the PIN screen as a lock screen (he likely wants telephony) and the
PIN screen is not shown on a timer-driven basis, it should be treated
specially.

Change-Id: I3572a80d4a515d72e3aa4a6e933e980fa4516c2b