Bug 860941 - Remove unnecessary argument cleanup in nsGlobalWindow::DetachFromDocShell. r=jst

This function proceeds to invoke CleanUp(), which also cleans this stuff up.

dom/base/nsGlobalWindow.cpp

@@ -2738,13 +2738,6 @@ nsGlobalWindow::DetachFromDocShell()
 
   mChromeEventHandler = nullptr; // force release now
 
-  if (mArguments) { 
-    // We got no new document after someone called
-    // SetArguments(), drop our reference to the arguments.
-    mArguments = nullptr;
-    mArgumentsOrigin = nullptr;
-  }
-
   if (mContext) {
     mContext->GC(JS::gcreason::SET_DOC_SHELL);
     mContext = nullptr;