Bug 1720314 - Part 1: Remove HTMLFormElement::mSubmittingRequest; r=smaug

Differential Revision: https://phabricator.services.mozilla.com/D119776

dom/html/HTMLFormElement.h

@@ -556,8 +556,6 @@ class HTMLFormElement final : public nsGenericHTMLElement,
 
   /** The pending submission object */
   UniquePtr<HTMLFormSubmission> mPendingSubmission;
-  /** The request currently being submitted */
-  nsCOMPtr<nsIRequest> mSubmittingRequest;
   /** The web progress object we are currently listening to */
   nsWeakPtr mWebProgress;