Remove hardcoded color for settings dashboard

1. Change card_background to default background color. In settings
light theme, background color is exactly the #fafafa
2. Change card_background_grey to colorSecondary, which is
material_grey_200 in settings light theme.

Bug: 36139640
Test: Screenshot
Change-Id: I20081e768985ce6c0b9000448ae48599f18b293a
diff --git a/res/layout/support_fragment.xml b/res/layout/support_fragment.xml
index 7c79a63..6864d32 100644
--- a/res/layout/support_fragment.xml
+++ b/res/layout/support_fragment.xml
@@ -27,6 +27,5 @@
     <android.support.v7.widget.RecyclerView
         android:id="@+id/support_items"
         android:layout_height="match_parent"
-        android:layout_width="match_parent"
-        android:background="@color/card_background"/>
+        android:layout_width="match_parent"/>
 </FrameLayout>