Don't give onboarding dialog a fixed width

Test: visual inspection (display and font largest)
Change-Id: Ia81cfa41c125d088d95db2e29f83248dc6819396
Fixes: 79960996
diff --git a/res/layout/zen_onboarding.xml b/res/layout/zen_onboarding.xml
index 82951bd..33cdbdd 100644
--- a/res/layout/zen_onboarding.xml
+++ b/res/layout/zen_onboarding.xml
@@ -16,8 +16,8 @@
 -->
 <RelativeLayout
     xmlns:android="http://schemas.android.com/apk/res/android"
-    android:layout_width="320dp"
-    android:layout_height="wrap_content" >
+    android:layout_width="match_parent"
+    android:layout_height="wrap_content">
 
     <RelativeLayout
         android:id="@+id/zen_onboarding_choices"