Do not define devture_traefik_provider_configuration_extension_yaml in group_vars/matrix_servers

`devture_traefik_provider_configuration_extension_yaml` should not be
set automatically by the playbook. It's a variable to be used by users.

Moreover, setting for for everyone (not just people who have additional JVBs)
means that for most people the following error will be produced:

> 'dict object' has no attribute 'jitsi_jvb_servers'

.. as detailed in https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/2844

Fixes a regression introduced in: https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/2842

group_vars/matrix_servers

@@ -2555,38 +2555,6 @@ jitsi_self_check_validate_certificates: "{{ false if matrix_ssl_retrieval_method
 # when embedding Jitsi in Matrix rooms.
 jitsi_disable_gravatar: true
 
-# Traefik proxying for additional JVBs. These can't be configured using Docker
-# labels, like the first JVB is, because they run on different hosts, so we add
-# the necessary configuration to the file provider.
-devture_traefik_provider_configuration_extension_yaml: |
-  http:
-   routers:
-     {% for host in groups['jitsi_jvb_servers'] %}
-
-     additional-{{ hostvars[host]['jitsi_jvb_server_id'] }}-router:
-       entryPoints:
-         - "{{ devture_traefik_entrypoint_primary }}"
-       rule: "Host(`{{ jitsi_hostname }}`) && PathPrefix(`/colibri-ws/{{ hostvars[host]['jitsi_jvb_server_id'] }}/`)"
-       service: additional-{{ hostvars[host]['jitsi_jvb_server_id'] }}-service
-       {% if devture_traefik_entrypoint_primary != 'web' %}
-
-       tls:
-         certResolver: "{{ devture_traefik_certResolver_primary }}"
-
-       {% endif %}
-
-     {% endfor %}
-
-   services:
-     {% for host in groups['jitsi_jvb_servers'] %}
-
-     additional-{{ hostvars[host]['jitsi_jvb_server_id'] }}-service:
-       loadBalancer:
-         servers:
-           - url: "http://{{ host }}:9090/"
-
-     {% endfor %}
-
 ######################################################################
 #
 # /jitsi