Code clean up

- Remove unused DashboardTilePreference class
- Use FooterPreference in ManageAssist fragment
- reformat manage_assist xml file

Bug: 35203386
Test: visual
Change-Id: If3dbbd0fb1977d6f3c7dbf4544d71f5e6e801327

src/com/android/settings/applications/ManageAssist.java

@@ -68,7 +68,8 @@ public class ManageAssist extends SettingsPreferenceFragment
 
         mFlashPref = (SwitchPreference) findPreference(KEY_FLASH);
         mFlashPref.setOnPreferenceChangeListener(this);
-
+        mFooterPreferenceMixin.createFooterPreference()
+                .setTitle(R.string.assist_footer);
         mVoiceInputPref = (VoiceInputListPreference) findPreference(KEY_VOICE_INPUT);
         updateUi();
     }