remove unreferenced target

CONTRIBUTING.md

@@ -146,7 +146,6 @@ just submit a pull request.
 * [Beginners Guide To Contributing](https://wiki.jenkins.io/display/JENKINS/Beginners+Guide+to+Contributing)
 * [List of newbie-friendly issues in the core](https://issues.jenkins-ci.org/issues/?jql=project%20%3D%20JENKINS%20AND%20status%20in%20(Open%2C%20%22In%20Progress%22%2C%20Reopened)%20AND%20component%20%3D%20core%20AND%20labels%20in%20(newbie-friendly))
 
-[download Maven]: https://maven.apache.org/download.cgi
 [Preparing for Plugin Development]: https://jenkins.io/doc/developer/tutorial/prepare/
 [newbie friendly issues]: https://issues.jenkins-ci.org/issues/?jql=project%20%3D%20JENKINS%20AND%20status%20in%20(Open%2C%20%22In%20Progress%22%2C%20Reopened)%20AND%20component%20%3D%20core%20AND%20labels%20in%20(newbie-friendly)
 [Participate]: https://jenkins.io/participate/