Recently I’ve been removing options from Spark to make it suitable for my clients to use. The way I went about finding out where things were in the source was to add the source to an IDE (I used Netbeans, but I’m sure other IDEs will be fine) and then use the IDE’s ability to search all the files in the project/projects folders (you could even use your operating system of choice to search within the project files). Search for the exact string that is in the menu item and it should take you to one of the internationalisation files (.properties) which in this case is the spark_i18n.properties file and specifically the text “menuitem.check.for.updates = Check For Updates”. Then search for menuitem.check.for.updates and you’ll find the exact place where the menu item is initialised. I’ve just been removing the call to add the menu item to the menu in these types of cases, but in other cases its worth checking nearby code to see if setting options on the client side will remove the ability or in few case setting a server side option get the result you want.
I haven’t looked into it yet myself, but, if you are using the Openfire server, you might want to try installing the Client Control plugin and using that to store and enforce the clients and client version that are able to be used. That way if you change the client they you could upload the new version to the server and when people connect it will notify them of the update. This is what the Client Control plugin seems to imply, but I haven’t tested it myself.
I hope this helps.