don't use system wide installed ocaml packages

Index: Makefile.config.in
--- Makefile.config.in.orig
+++ Makefile.config.in
@@ -14,7 +14,6 @@ OCAMLFIND = @OCAMLFIND@
 OCAML = @OCAML@
 OCAMLC = @OCAMLC@
 OCAMLOPT = @OCAMLOPT@
-DUNE = @DUNE@
 DUNE_SECONDARY = @DUNE_SECONDARY@
 LN_S = @LN_S@
 
