MEDIUM: Make 'block' directive fatal

It was deprecated with HAProxy 1.5. Time to remove it.
diff --git a/include/types/global.h b/include/types/global.h
index f9ab4c2..fb0c5e1 100644
--- a/include/types/global.h
+++ b/include/types/global.h
@@ -249,7 +249,7 @@
 extern int atexit_flag;
 
 /* bit values to go with "warned" above */
-#define WARN_BLOCK_DEPRECATED       0x00000001
+/* unassigned : 0x00000001 (previously: WARN_BLOCK_DEPRECATED) */
 /* unassigned : 0x00000002 */
 #define WARN_REDISPATCH_DEPRECATED  0x00000004
 #define WARN_CLITO_DEPRECATED       0x00000008