Fix double-quoting in /.well-known/matrix/support

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/1931

`|to_json` already adds the surrounding double-quotes for the string, so
adding them explicitly means we've got a double-quotes problem.

roles/matrix-base/templates/static-files/well-known/matrix-support.j2

@@ -2,6 +2,6 @@
 {
     "admins": {{ matrix_homeserver_admin_contacts|to_json }}
     {% if matrix_homeserver_support_url %},
-        "support_page": "{{ matrix_homeserver_support_url|to_json }}"
+        "support_page": {{ matrix_homeserver_support_url|to_json }}
     {% endif %}
 }