You can uninstall or removes an installed libjava-xmlbuilder-java package itself from Ubuntu 16.04 LTS (Xenial Xerus) through the terminal,
$ sudo apt-get remove libjava-xmlbuilder-java
If you would like to remove libjava-xmlbuilder-java and it's dependent packages which are no longer needed from Ubuntu,
$ sudo apt-get remove --auto-remove libjava-xmlbuilder-java
If you use with purge options to libjava-xmlbuilder-java package all the configuration and dependent packages will be removed.
$ sudo apt-get purge libjava-xmlbuilder-java
If you use purge options along with auto remove, will be removed everything regarding the package, It's really useful when you want to reinstall again.
$ sudo apt-get purge --auto-remove libjava-xmlbuilder-java