Don't back up / restore "allow apps from unknown sources"

We no longer back up the state of the "Allow the installation of applications
from unknown sources" setting, nor do we set that based on restore data even if
it is present.

Change-Id: Ida276874616f1ff82807d642b0b733fcab339529

core/java/android/provider/Settings.java

@@ -2405,7 +2405,6 @@ public final class Settings {
         public static final String[] SETTINGS_TO_BACKUP = {
             ADB_ENABLED,
             ALLOW_MOCK_LOCATION,
-            INSTALL_NON_MARKET_APPS,
             PARENTAL_CONTROL_ENABLED,
             PARENTAL_CONTROL_REDIRECT_URL,
             USB_MASS_STORAGE_ENABLED,