You can uninstall or removes an installed libx11-protocol-perl package itself from Ubuntu 14.04 LTS (Trusty Tahr) through the terminal,
$ sudo apt-get remove libx11-protocol-perl
If you would like to remove libx11-protocol-perl and it's dependent packages which are no longer needed from Ubuntu,
$ sudo apt-get remove --auto-remove libx11-protocol-perl
If you use with purge options to libx11-protocol-perl package all the configuration and dependent packages will be removed.
$ sudo apt-get purge libx11-protocol-perl
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 libx11-protocol-perl