DisplaySettings: Remove override function + Fix derp

```
packages/apps/Settings/src/com/android/settings/DisplaySettings.java:111: isPackageInstalled(java.lang.String) in com.android.settings.DisplaySettings cannot override isPackageInstalled(java.lang.String) in com.android.settings.SettingsPreferenceFragment; attempting to assign weaker access privileges; was public
private boolean isPackageInstalled(String packagename) {
^
```
    packages/apps/Settings/src/com/android/settings/DisplaySettings.java:517: illegal start of expression