disable "build by token" by default using a system property in Jenkins

Jenkins has ACLs and you need to have read access in order to find the build to trigger so this should be removed as it creates confusion and can be handled by granting the user Item.BUILD

For post commit hooks they should post to global hook (e.g. svn hook or git hook url),
for other systems if special anonymous access to trigger a build is required a new plugin should be introduced.

The backend code was marked as deprecated with the early versions of Hudson (> 10 years ago) yet there is nothing in the UI to show this is the case.