Remove the Sigma (monotonous state) API.

Reminder of (some of) the reasons for removal:

- Despite the claim in sigma.mli, it does *not* prevent evar
  leaks, something like:

  fun env evd ->
  let (evd',ev) = new_evar env evd in
  (evd,ev)

  will typecheck even with Sigma-like type annotations (with a proof of
  reflexivity)

- The API stayed embryonic. Even typing functions were not ported to
  Sigma.

- Some unsafe combinators (Unsafe.tclEVARS) were replaced with slightly
  less unsafe ones (e.g. s_enter), but those ones were not marked unsafe
  at all (despite still being so).

- There was no good story for higher order functions manipulating evar
  maps. Without higher order, one can most of the time get away with
  reusing the same name for the updated evar map.

- Most of the code doing complex things with evar maps was using unsafe
  casts to sigma. This code should be fixed, but this is an orthogonal
  issue.

Of course, this was showing a nice and elegant use of GADTs, but the
cost/benefit ratio in practice did not seem good.

1 files changed, 2 insertions, 3 deletions

diff --git a/plugins/ltac/g_rewrite.ml4 b/plugins/ltac/g_rewrite.ml4
index 5adf8475a..25258ffa9 100644
--- a/plugins/ltac/g_rewrite.ml4
+++ b/plugins/ltac/g_rewrite.ml4
@@ -18,7 +18,6 @@ open Glob_term
 open Geninterp
 open Extraargs
 open Tacmach
-open Proofview.Notations
 open Rewrite
 open Stdarg
 open Pcoq.Vernac_
@@ -123,7 +122,7 @@ TACTIC EXTEND rewrite_strat
 END
 
 let clsubstitute o c =
-  Proofview.Goal.enter { enter = begin fun gl ->
+  Proofview.Goal.enter begin fun gl ->
   let is_tac id = match fst (fst (snd c)) with { CAst.v = GVar id' } when Id.equal id' id -> true | _ -> false in
   let hyps = Tacmach.New.pf_ids_of_hyps gl in
     Tacticals.New.tclMAP
@@ -132,7 +131,7 @@ let clsubstitute o c =
           | Some id when is_tac id -> Tacticals.New.tclIDTAC
           | _ -> cl_rewrite_clause c o AllOccurrences cl)
       (None :: List.map (fun id -> Some id) hyps)
-  end }
+  end
 
 TACTIC EXTEND substitute
 | [ "substitute" orient(o) glob_constr_with_bindings(c) ] -> [ clsubstitute o c ]