haproxy: http-send-name-header no longer needed

- destination server gets its own server id
- this removes complexity at the cost of respecting consistency in names
- http-send-name-header is not well supported by haproxy and that it may leads to random errors with not well formated request

/reviewed-on nexedi/slapos!324

stack/erp5/buildout.hash.cfg

@@ -95,4 +95,4 @@ md5sum = 29cfe35d37cf615378574707978e5f75
 
 [template-haproxy-cfg]
 filename = haproxy.cfg.in
-md5sum = 3defd473e2cea17ae36bba7752494858
+md5sum = 13f1f731ec941f4ba941d6fa8834a5cc

stack/erp5/haproxy.cfg.in

@@ -12,7 +12,6 @@ defaults
   option redispatch
   maxconn 2000
   cookie SERVERID rewrite
-  http-send-name-header X-Balancer-Current-Server
   balance roundrobin
   stats uri /haproxy
   stats realm Global\ statistics