You'll need to amend the vm files that display them in various places - the main one is "footer.vm" where you can remove the version display from every page (but you must not remove the link that says "powered by atlassian Jira/confluence". The other place is the help -> about menu, but I don't know what files to look for there, I've never had any desire to remove the information.
I should also point out that this is "security by obscurity" - there are plenty of other ways of finding out the versions of the services and components, all you would be doing is making it slightly less obvious.
