You can uninstall or removes an installed libxmpi4-dev package itself from Ubuntu 14.04 LTS (Trusty Tahr) through the terminal,
$ sudo apt-get remove libxmpi4-dev
If you would like to remove libxmpi4-dev and it's dependent packages which are no longer needed from Ubuntu,
$ sudo apt-get remove --auto-remove libxmpi4-dev
If you use with purge options to libxmpi4-dev package all the configuration and dependent packages will be removed.
$ sudo apt-get purge libxmpi4-dev
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 libxmpi4-dev