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