You can uninstall or removes an installed gdc-6-mips64-linux-gnuabi64 package itself from Ubuntu 17.04 (Zesty Zapus) through the terminal,
$ sudo apt-get remove gdc-6-mips64-linux-gnuabi64
If you would like to remove gdc-6-mips64-linux-gnuabi64 and it's dependent packages which are no longer needed from Ubuntu,
$ sudo apt-get remove --auto-remove gdc-6-mips64-linux-gnuabi64
If you use with purge options to gdc-6-mips64-linux-gnuabi64 package all the configuration and dependent packages will be removed.
$ sudo apt-get purge gdc-6-mips64-linux-gnuabi64
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 gdc-6-mips64-linux-gnuabi64