Remove the parentURIContentListener attribute on docshell; people not using

nsIWebBrowser can getInterface the docshells nsIURIContentListener and set its
parent.  Bug 283108, r=biesi, sr=darin

suite/browser/nsBrowserContentListener.js

@@ -59,8 +59,14 @@ nsBrowserContentListener.prototype =
 
         // hook up the whole parent chain thing
         var windowDocShell = this.convertWindowToDocShell(toplevelWindow);
-        if (windowDocShell)
-            windowDocshell.parentURIContentListener = this;
+        if (windowDocShell) {
+            // XXXbz this listener is never unregistered.  Did someone neglect 
+            // to read the interface they're using?
+            windowDocshell
+              .QueryInterface(Components.interfaces.nsIInterfaceRequestor)
+              .getInterface(Components.interfaces.nsIURIContentListener)
+              .parentContentListener = this;
+        }
 
         var registerWindow = false;
         try {