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