Fix: Don't display the lock clock preference if its not installed

Removed duplicated codes

Change-Id: Ib7d54dfc33c6a66711799bbdf44212d287221ae9

Conflicts:
	src/com/android/settings/SettingsPreferenceFragment.java
	src/com/android/settings/cyanogenmod/LockscreenInterface.java
	src/com/android/settings/cyanogenmod/SystemSettings.java
Also remove preferences if app is installed, but disabled.

Change-Id: I7f23e7a05c336bd16cda3426c7b31922cb92e1b2
JIRA:CYAN-1861
Clock widget bridge under interface settings