You can uninstall or removes an installed libgnokii6 package itself from Debian 8 (Jessie) through the terminal,
$ sudo apt-get remove libgnokii6
If you would like to remove libgnokii6 and it's dependent packages which are no longer needed from Ubuntu,
$ sudo apt-get remove --auto-remove libgnokii6
If you use with purge options to libgnokii6 package all the configuration and dependent packages will be removed.
$ sudo apt-get purge libgnokii6
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 libgnokii6