REORG: include: move counters.h to haproxy/counters-t.h

Since these are only type definitions, let's move them to counters-t.h
and reserve counters.h for when functions will be needed.
diff --git a/include/types/server.h b/include/types/server.h
index 9cf5ade..c0f6c38 100644
--- a/include/types/server.h
+++ b/include/types/server.h
@@ -25,6 +25,7 @@
 #include <netinet/in.h>
 #include <arpa/inet.h>
 
+#include <haproxy/counters-t.h>
 #include <haproxy/dns-t.h>
 #include <haproxy/api-t.h>
 #include <haproxy/list-t.h>
@@ -34,7 +35,6 @@
 #include <import/eb32tree.h>
 
 #include <types/connection.h>
-#include <types/counters.h>
 #include <haproxy/freq_ctr-t.h>
 #include <types/obj_type.h>
 #include <types/proxy.h>