More code cleaning

- remove some dead code
- better variable naming
- add debug log for exception
- clean some unused imports

Change-Id: Iec4239a7e75f29d860f286ab089e748e8a672281

src/com/android/settings/SubSettings.java

@@ -16,11 +16,8 @@
 
 package com.android.settings;
 
-import android.app.Fragment;
 import android.util.Log;
 
-import com.android.settings.ChooseLockGeneric.ChooseLockGenericFragment;
-
 /**
  * Stub class for showing sub-settings; we can't use the main Settings class
  * since for our app it is a special singleTask class.