[wp] Plugin reduc: removes an unused field to avoid a warning with ocaml 4.13.

src/plugins/reduc/collect.ml

@@ -39,14 +39,14 @@ type varh = VarAll
 type annoth = AnnotAll | AnnotInout
 
 type env = {
-  rel_varh: varh;
+  (* rel_varh: varh; *)
   rel_annoth: annoth;
   rel_stmts: Stmt.Set.t;
   rel_vars: LvalStructEq.Set.t Stmt.Map.t;
 }
 
-let empty_env varh annoth = {
-  rel_varh = varh;
+let empty_env _varh annoth = {
+  (* rel_varh = varh; *)
   rel_annoth = annoth;
   rel_stmts = Stmt.Set.empty;
   rel_vars = Stmt.Map.empty;