Use FooterPreference in xml explicitly

Removed the FooterPreferenceMixin from the TetherSettings page.

Fixes: 139397226
Test: manual test
Change-Id: Ice7f97881df9cc17177ed7fcc1da9f3124c445a9

res/xml/tether_prefs.xml

@@ -44,4 +44,10 @@
         android:summary="@string/tether_settings_disabled_on_data_saver"
         android:selectable="false"
         settings:allowDividerAbove="true" />
+
+    <com.android.settingslib.widget.FooterPreference
+        android:key="tether_prefs_footer"
+        android:title="@string/tethering_footer_info"
+        android:selectable="false"
+        settings:searchable="false"/>
 </PreferenceScreen>

src/com/android/settings/TetherSettings.java

@@ -120,9 +120,6 @@ public class TetherSettings extends RestrictedSettingsFragment
         super.onCreate(icicle);
 
         addPreferencesFromResource(R.xml.tether_prefs);
-        mFooterPreferenceMixin.createFooterPreference()
-            .setTitle(R.string.tethering_footer_info);
-
         mDataSaverBackend = new DataSaverBackend(getContext());
         mDataSaverEnabled = mDataSaverBackend.isDataSaverEnabled();
         mDataSaverFooter = findPreference(KEY_DATA_SAVER_FOOTER);