GeoHelm can be removed like any other Webmin Module.
Simply navigate to Webmin > Webmin Configuration > Modules.
From here, you can remove the module.
Note that all components (Tomcat, Java, GeoServer, Apache, PostGIS, etc...) will continue to function as normal.
If you wish to remove all components:
/home/tomcat
directory and all sub directories./usr/java
directory and all sub directories/etc/environment
file to remove all paths.