Use syntax extension for parsing stanza

Signed-off-by: Rudi Grinberg <rudi.grinberg@gmail.com>

src/dune_env.ml

@@ -1,7 +1,6 @@
 type stanza = Stanza.t = ..
 
 module Stanza = struct
-  open Import
   open Stanza.Of_sexp
 
   let field_oslu name = Ordered_set_lang.Unexpanded.field name
@@ -38,9 +37,10 @@ module Stanza = struct
        (pat, configs))
 
   let t =
-    Syntax.since Stanza.syntax (1, 0) >>= fun () ->
-    loc >>= fun loc ->
-    repeat rule >>| fun rules ->
+    let%map () = Syntax.since Stanza.syntax (1, 0)
+    and loc = loc
+    and rules = repeat rule
+    in
     { loc; rules }
 
 end

src/jbuild.ml

@@ -1592,7 +1592,9 @@ module Stanzas = struct
       (let%map () = Syntax.since Stanza.syntax (1, 0)
        and t = Tests.single in
        [Tests t])
-    ; "env", Dune_env.Stanza.t >>| fun x -> [Dune_env.T x]
+    ; "env",
+      (let%map x = Dune_env.Stanza.t in
+       [Dune_env.T x])
     ]
 
   let jbuild_parser =