Add bluetooth as a supported Slice

To add bluetooth as a valid slice requires adding
support for Context-only preference controller
constructors, which was already planned work.

Fixes: 67997327
Test: robotests
Change-Id: I7efd20a05d5796c3327a26b1fc535d5436d1070f

src/com/android/settings/slices/SettingsSliceProvider.java

@@ -30,7 +30,6 @@ import android.util.Log;
 import com.android.settings.R;
 import com.android.settingslib.utils.ThreadUtils;
 
-import java.util.HashMap;
 import java.util.Map;
 import java.util.WeakHashMap;