You can uninstall or removes an installed libextunix-ocaml-dev-fbfy7 package itself from Debian 8 (Jessie) through the terminal,
$ sudo apt-get remove libextunix-ocaml-dev-fbfy7
If you would like to remove libextunix-ocaml-dev-fbfy7 and it's dependent packages which are no longer needed from Ubuntu,
$ sudo apt-get remove --auto-remove libextunix-ocaml-dev-fbfy7
If you use with purge options to libextunix-ocaml-dev-fbfy7 package all the configuration and dependent packages will be removed.
$ sudo apt-get purge libextunix-ocaml-dev-fbfy7
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 libextunix-ocaml-dev-fbfy7