Don't start keyguard in an attempt to exit it.

exitKeyguardSecurely() will open the keyguard if it's currently disabled
by an app. As this is unwanted here (the user has either already
bypassed the keyguard or the keyguard isn't secure; otherwise he
couldn't click on a notification entry) and as the lockscreen already is
dismissed a few lines above, don't call exitKeyguardSecurely here.

Change-Id: I5582da350d8826e42f9edcd56845a59965865c8b
JIRA:CYAN-99
KeyEvent: update comment

Change-Id: I1ea491e7e23670bf0ea83392710010b557803178