Bug 732877: Remove no-longer-used variable 'oldPrincipal' from nsGlobalWindow.cpp. r=jst

dom/base/nsGlobalWindow.cpp

@@ -1933,12 +1933,6 @@ nsGlobalWindow::SetNewDocument(nsIDocument* aDocument,
 
   bool reUseInnerWindow = aForceReuseInnerWindow || wouldReuseInnerWindow;
 
-  // Remember the old document's principal.
-  nsIPrincipal *oldPrincipal = nsnull;
-  if (oldDoc) {
-    oldPrincipal = oldDoc->NodePrincipal();
-  }
-
   nsresult rv = NS_OK;
 
   // Set mDocument even if this is an outer window to avoid