infra: avoid outdated local checkstyle ZIPs

After version upgrades outdated ZIP files from former versions can
remain in the local git repository. Get rid of all but the current
version when building.

Author: Bananeweizen

net.sf.eclipsecs.checkstyle/pom.xml

@@ -24,6 +24,10 @@
                         <phase>generate-sources</phase>
                         <configuration>
                             <target>
+                                <!-- delete all the outdated ZIPs before downloading the current -->
+                                <delete>
+                                    <fileset dir="${basedir}" includes="checkstyle-*.zip" excludes="checkstyle-${checkstyle.version}.zip"/>
+                                </delete>
                                 <get src="https://github.com/checkstyle/checkstyle/archive/checkstyle-${checkstyle.version}.zip"
                                      dest="${basedir}/checkstyle-${checkstyle.version}.zip"
                                      verbose="false"