archwiki: use a drop-in file for memcached@.service instead of an entirely custom unit

This allows to retain all default hardening options that memcached@.service has.

group_vars/all/archusers.yml

@@ -265,13 +265,6 @@ arch_users:
     shell: /bin/zsh
     groups:
       - tu
-  fukawi2:
-    name: "Phillip Smith"
-    ssh_key: fukawi2.pub
-    hosts:
-      - mail.archlinux.org
-    groups:
-      - support-staff
   gitlab:
     name: ""
     groups: []