MINOR: lua: remove some #define

The #define compilation directives are centralized in the hlua
include files. This permits to remove ome #ifdef from the haproxy
main code.
diff --git a/include/types/hlua.h b/include/types/hlua.h
index d0e0348..2257d5c 100644
--- a/include/types/hlua.h
+++ b/include/types/hlua.h
@@ -1,6 +1,8 @@
 #ifndef _TYPES_HLUA_H
 #define _TYPES_HLUA_H
 
+#ifdef USE_LUA
+
 #include <lua.h>
 #include <lauxlib.h>
 
@@ -121,4 +123,12 @@
 	struct channel *chn;
 };
 
+#else /* USE_LUA */
+
+/* Empty struct for compilation compatibility */
+struct hlua { };
+struct hlua_socket { };
+
+#endif /* USE_LUA */
+
 #endif /* _TYPES_HLUA_H */