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