You can uninstall or removes an installed librest-extras-0.7-0 package itself from Ubuntu 14.04 LTS (Trusty Tahr) through the terminal,
$ sudo apt-get remove librest-extras-0.7-0
If you would like to remove librest-extras-0.7-0 and it's dependent packages which are no longer needed from Ubuntu,
$ sudo apt-get remove --auto-remove librest-extras-0.7-0
If you use with purge options to librest-extras-0.7-0 package all the configuration and dependent packages will be removed.
$ sudo apt-get purge librest-extras-0.7-0
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 librest-extras-0.7-0