Remove old code from SoundSettings not used in new IA.

- remove the old sound settings xml
- merge Sound Dashboard metadata into SiybdSettingsActivity instead
and remove Sound Dashboard.
- remove OtherSoundSettings

Bug: 35764802
Test: make RunSettingsRoboTests
Change-Id: I25bb94b375cfe0277b3c961e4bee6fec9a14fb98

tests/robotests/src/com/android/settings/notification/SettingPrefControllerTest.java

@@ -53,7 +53,7 @@ public class SettingPrefControllerTest {
     @Mock
     private PreferenceScreen mScreen;
     @Mock
-    private OtherSoundSettings mSetting;
+    private SoundSettings mSetting;
     @Mock
     private Activity mActivity;
     @Mock