[css-nav-1] Modify the inheritance of spatial-navigation-function

Reason: This property is equivalent with `spatial-navigation-action` in terms of inheritance feature

Author: Jihye Hong

css-nav-1/Overview.bs

@@ -1576,7 +1576,7 @@ Name: spatial-navigation-function
 Value: normal | grid
 Initial: normal
 Applies to: <a>spatial navigation container</a>
-Inherited: yes
+Inherited: no
 </pre>
 
 The default algorithm of spatial navigation specified in the [[#processing-model]] may need the fine tune depending on the layout types.