Reduce number of wallpaper results in search.

Previously we indexed the intent in display settings and every
app that handled ACTION_SET_WALLPAPER. Now, we only index an
app that handles ACTION_SET_WALLPAPER and is the listed package in
config_wallpaper_picker_package.

Change-Id: Ife81702017e3e8be4a754873d9c453fddf1cbd9e
Fixes: 62793068
Test: manual, search wallpaper and observe results

src/com/android/settings/DisplaySettings.java

@@ -127,6 +127,7 @@ public class DisplaySettings extends DashboardFragment {
                 public List<String> getNonIndexableKeys(Context context) {
                     List<String> keys = super.getNonIndexableKeys(context);
                     keys.add(KEY_DISPLAY_SIZE);
+                    keys.add(WallpaperPreferenceController.KEY_WALLPAPER);
                     return keys;
                 }