remove some obsolete update css file references

mail/base/content/mailWindowOverlay.xul

@@ -38,8 +38,6 @@
 
 <?xml-stylesheet href="chrome://messenger/skin/folderMenus.css" type="text/css"?>
 <?xml-stylesheet href="chrome://communicator/skin/tasksOverlay.css" type="text/css"?> 
-<?xml-stylesheet href="chrome://mozapps/skin/extensions/update.css" type="text/css"?> 
-<?xml-stylesheet href="chrome://mozapps/content/update/updates.css" type="text/css"?> 
 
 <?xul-overlay href="chrome://global/content/charsetOverlay.xul"?>
 <?xul-overlay href="chrome://messenger/content/mailWindowExtrasOverlay.xul"?>