Remove org dependency

This dependency installs the `org` package even if I already have the `org-plus-contrib` one.

I don't know if there's a way to depends on one or the other but I think most packages don't list `org` as a dependency. See https://github.com/nsf/gocode/blob/71ddfa9f5e27550498120f39b34bb79f8cfcc7fe/emacs-company/company-go.el#L7