Misc clean up in search

- Remove updateFromClassNameResource() because it's just a no-op method.
- Simplify SearchIndexResources
- Update some pref pages to have unique keys.

Change-Id: I51e542d9947aafd046861ce7be0b4c7213fcd01d
Fixes: 64951285
Test: UniquePreferenceKeyTest
Test: robotest
Bug: 67852637

tests/robotests/src/com/android/settings/search/XmlParserUtilTest.java

@@ -120,6 +120,7 @@ public class XmlParserUtilTest {
 
     // Null checks
     @Test
+    @Config(qualifiers = "mcc999")
     public void testDataKeyInvalid_ReturnsNull() {
         XmlResourceParser parser = getParentPrimedParser(R.xml.display_settings);
         final AttributeSet attrs = Xml.asAttributeSet(parser);