For more information see the official ProGuard Website
To enable the build of proguard-wtk-plugin you have to do the following:
- Install the WTK2.2 (Java 1.4+ is required) from Oracle Download Page
- Specify the property "wireless-toolkit-path" in your %HOME%/.m2/settings.xml file and let it point to the WTK installation directory
- If specified correctly the next Maven build should include the proguard-wtk-plugin