Meta: markup [PrimaryGlobal] as only an extended attribute

This erroneous markup, which indicated [PrimaryGlobal] was both an "extended-attribute" definition and a "dfn" definition, will not work in an upcoming revision of Bikeshed.

Author: tabatkins

index.bs

@@ -9235,7 +9235,7 @@ for the specific requirements that the use of
 </div>
 
 
-<h4 oldids="PrimaryGlobal" id="Global" extended-attribute lt="Global" dfn>[Global]</h4>
+<h4 oldids="PrimaryGlobal" id="Global" extended-attribute lt="Global">[Global]</h4>
 
 If the [{{Global}}] [=extended attribute=] appears on an [=interface=],
 it indicates that objects implementing this interface can