Stop using unstable repos to install wireguard

It's in backports now, which is much easier to install from!

ansible/roles/gateway/files/limit-unstable.conf

@@ -1,3 +0,0 @@
-Package: *
-Pin: release a=unstable
-Pin-Priority: 90

ansible/roles/gateway/tasks/wireguard.yml

@@ -1,31 +1,3 @@
-- name: Add unstable apt repo
-  lineinfile:
-    path: /etc/apt/sources.list.d/unstable.list
-    state: present
-    line: deb http://deb.debian.org/debian/ unstable main
-  register: install_unstable_apt
-  become: true
-
-- name: Limit unstable apt repo
-  copy:
-    src: limit-unstable.conf
-    dest: /etc/apt/preferences.d/limit-unstable
-  become: true
-  register: limit_unstable_apt
-
-- name: Update apt repos
-  apt:
-    update_cache: true
-  become: true
-  when: install_unstable_apt.changed or limit_unstable_apt.changed
-
-- name: Install Wireguard
-  apt:
-    name:
-      - wireguard
-      - wireguard-tools
-  become: true
-
 - name: Wireguard server config
   template:
     src: files/wireguard-server.conf