Remove _matrix._tcp.archlinux.org SRV record

The `https://archlinux.org/.well-known/matrix/server` response is used
over the SRV record in all cases. We haven't been listening on 8448
since e9e4c114 (June 2019).

tf-stage1/archlinux.tf

@@ -457,13 +457,6 @@ resource "hetznerdns_record" "archlinux_org_origin_ns1" {
 #   type = "SOA"
 # }
 
-resource "hetznerdns_record" "archlinux_org_matrix_tcp_srv" {
-  zone_id = hetznerdns_zone.archlinux.id
-  name    = "_matrix._tcp"
-  value   = "10 0 8448 matrix"
-  type    = "SRV"
-}
-
 resource "hcloud_floating_ip" "gitlab_pages" {
   type        = "ipv4"
   description = "GitLab Pages"