Bug 1631548 - part 2: Remove nsGenericHTMLFrameElement::mFrameLoaderCreationDisallowed. r=emilio

Setters for this field are removed in the previous commit.
This field is always false. We can remove it.

Differential Revision: https://phabricator.services.mozilla.com/D71630

dom/html/nsGenericHTMLFrameElement.cpp

@@ -121,7 +121,7 @@ Nullable<WindowProxyHolder> nsGenericHTMLFrameElement::GetContentWindow() {
 }
 
 void nsGenericHTMLFrameElement::EnsureFrameLoader() {
-  if (!IsInComposedDoc() || mFrameLoader || mFrameLoaderCreationDisallowed) {
+  if (!IsInComposedDoc() || mFrameLoader) {
     // If frame loader is there, we just keep it around, cached
     return;
   }