[gedit-plugins] Remove CONTRIBUTING.md, outdated and no longer needed

[Sébastien Wilmet <swilmet src gnome org>]

commit 9bec02f15a9a4971facaa59557ecd98164385c11
Author: Sébastien Wilmet <swilmet gnome org>
Date:   Tue Sep 3 18:38:58 2019 +0200

    Remove CONTRIBUTING.md, outdated and no longer needed
    
    It explained to send patches on bugzilla! We are now on GitLab.
    
    And there is now a script dealing with pull requests on the GitHub
    mirror of GNOME repos, explaining that it is not the right place where
    to contribute.

 CONTRIBUTING.md | 6 ------
 1 file changed, 6 deletions(-)