Use a released version of maven-hpi-plugin

This is using an rc coming from
jenkinsci/maven-hpi-plugin#464 which fails
locally when there are no github credentials.

If jenkinsci#464 is really needed it should be released (probably behind a flag).

prep.sh

@@ -38,7 +38,6 @@ for LINE in $LINEZ; do
 			${PROFILE:-} \
 			-DoverrideWar="../target/megawar-${LINE}.war" \
 			-DuseUpperBounds \
-			-Dhpi-plugin.version=3.42-rc1409.669de6d1a_866 \
 			-DcommitHashes=target/commit-hashes.txt
 		mv sample-plugin/target/commit-hashes.txt "target/commit-hashes-${LINE}.txt"
 	fi