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