[FIXED JENKINS-23364] make plugin available with goal prefix "jenkins-dev"

The goals in *maven-jenkins-dev-plugin* are available as e.g. `mvn hudson-dev:run` out of the box while using `mvn jenkins-dev:run` requires users to configure *org.jenkins-ci.tools* as a *pluginGroup* in maven's *settings.xml*.

This is not obvious (after all, it's the **jenkins-dev**-plugin) and no longer appropriate.

This PR removes the explicitely configured *goalPrefix* of *hudson-dev* so that the automatically assigned prefix of *jenkins-dev* becomes available.

There is one drawback, though: the goals will no longer work with the legacy prefix of *hudson-dev*.
IMHO, this is acceptable.

See https://issues.jenkins-ci.org/browse/JENKINS-23364