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