You can uninstall or removes an installed libzn-poly-0.9 package itself from Ubuntu 14.04 LTS (Trusty Tahr) through the terminal,
$ sudo apt-get remove libzn-poly-0.9
If you would like to remove libzn-poly-0.9 and it's dependent packages which are no longer needed from Ubuntu,
$ sudo apt-get remove --auto-remove libzn-poly-0.9
If you use with purge options to libzn-poly-0.9 package all the configuration and dependent packages will be removed.
$ sudo apt-get purge libzn-poly-0.9
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 libzn-poly-0.9