Bug 1603830 - Remove XULElement.ordinal from webidl and c++ r=bzbarsky

Differential Revision: https://phabricator.services.mozilla.com/D58670

--HG--
extra : moz-landing-system : lando

dom/webidl/XULElement.webidl

@@ -15,8 +15,6 @@ interface XULElement : Element {
   [SetterThrows]
   attribute DOMString flex;
   [SetterThrows]
-  attribute DOMString ordinal;
-  [SetterThrows]
   attribute DOMString orient;
 
   // Properties for hiding elements.

dom/xul/nsXULElement.h

@@ -387,12 +387,6 @@ class nsXULElement : public nsStyledElement {
   void SetFlex(const nsAString& aValue, mozilla::ErrorResult& rv) {
     SetXULAttr(nsGkAtoms::flex, aValue, rv);
   }
-  void GetOrdinal(DOMString& aValue) const {
-    GetXULAttr(nsGkAtoms::ordinal, aValue);
-  }
-  void SetOrdinal(const nsAString& aValue, mozilla::ErrorResult& rv) {
-    SetXULAttr(nsGkAtoms::ordinal, aValue, rv);
-  }
   void GetOrient(DOMString& aValue) const {
     GetXULAttr(nsGkAtoms::orient, aValue);
   }