You can uninstall or removes an installed gtkpod package itself from Ubuntu 16.04 LTS (Xenial Xerus) through the terminal,
$ sudo apt-get remove gtkpod
If you would like to remove gtkpod and it's dependent packages which are no longer needed from Ubuntu,
$ sudo apt-get remove --auto-remove gtkpod
If you use with purge options to gtkpod package all the configuration and dependent packages will be removed.
$ sudo apt-get purge gtkpod
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 gtkpod