Bug 1596506 - Remove special-case for <xul:label> accesskey. r=smaug

We don't have any NAC which is a <xul:label>. We could keep it for shadow dom but it
doesn't seem to me like this code is working correctly.

nsXULLabelFrame::RegUnregAccessKey doesn't have similar code, and uses the
<label> node to register / unregister.

Finally, we do have non-anon labels, and those would be broken... So just
remove the special-case.

Depends on D53058

Differential Revision: https://phabricator.services.mozilla.com/D53059

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

dom/xul/nsXULElement.cpp

@@ -707,24 +707,9 @@ void nsXULElement::UnregisterAccessKey(const nsAString& aOldValue) {
   //
   Document* doc = GetComposedDoc();
   if (doc && !aOldValue.IsEmpty()) {
-    PresShell* presShell = doc->GetPresShell();
-
-    if (presShell) {
-      Element* element = this;
-
-      // find out what type of content node this is
-      if (mNodeInfo->Equals(nsGkAtoms::label)) {
-        // For anonymous labels the unregistering must
-        // occur on the binding parent control.
-        // XXXldb: And what if the binding parent is null?
-        nsIContent* bindingParent = GetBindingParent();
-        element = bindingParent ? bindingParent->AsElement() : nullptr;
-      }
-
-      if (element) {
-        presShell->GetPresContext()->EventStateManager()->UnregisterAccessKey(
-            element, aOldValue.First());
-      }
+    if (PresShell* presShell = doc->GetPresShell()) {
+      presShell->GetPresContext()->EventStateManager()->UnregisterAccessKey(
+          this, aOldValue.First());
     }
   }
 }