remove unused strings

sample/src/main/res/values/strings.xml

@@ -124,11 +124,8 @@
         <item>Wisconsin</item>
         <item>Wyoming</item>
     </string-array>
-    <string name="title_activity_preference">PreferenceActivity</string>
 
+    <string name="title_activity_preference">PreferenceActivity</string>
     <string name="Preference_Dialog">Preference Dialog</string>
 
-    <string name="hello_world">Hello world!</string>
-    <string name="action_settings">Settings</string>
-
 </resources>