remove unused mailman role

The redirects are now done by the `redirects` role.

roles/mailman/tasks/main.yml

----
-
-- name: set up nginx
-  template: src=nginx.d.conf.j2 dest=/etc/nginx/nginx.d/mailman.conf owner=root group=root mode=644
-  notify:
-    - reload nginx
-  tags:
-    - nginx
-
-- name: make nginx log dir
-  file: path=/var/log/nginx/{{ mailman_domain }} state=directory owner=root group=root mode=0755
-  when: archweb_site
-  tags:
-    - nginx

roles/mailman/templates/nginx.d.conf.j2

-server {
-    listen       80;
-    listen       [::]:80;
-    server_name  mailman.archlinux.org;
-
-    access_log   /var/log/nginx/{{ mailman_domain }}/access.log reduced;
-    access_log   /var/log/nginx/{{ mailman_domain }}/access.log.json json_reduced;
-    error_log    /var/log/nginx/{{ mailman_domain }}/error.log;
-
-    include snippets/letsencrypt.conf;
-
-    location / {
-        access_log off;
-        return 301 https://{{ mailman_domain }}$request_uri;
-    }
-}
-
-server {
-    listen       443 ssl http2;
-    listen       [::]:443 ssl http2;
-    server_name  mailman.archlinux.org;
-
-    access_log   /var/log/nginx/{{ mailman_domain }}/access.log reduced;
-    access_log   /var/log/nginx/{{ mailman_domain }}/access.log.json json_reduced;
-    error_log    /var/log/nginx/{{ mailman_domain }}/error.log;
-
-    ssl_certificate      /etc/letsencrypt/live/mailman.archlinux.org/fullchain.pem;
-    ssl_certificate_key  /etc/letsencrypt/live/mailman.archlinux.org/privkey.pem;
-    ssl_trusted_certificate /etc/letsencrypt/live/mailman.archlinux.org/chain.pem;
-
-    location / {
-        access_log off;
-        return 301 https://{{ mailman_domain }}$request_uri;
-    }
-}