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, 3 insertions, 7 deletions

diff --git a/proofs/clenv.ml b/proofs/clenv.ml
index d6ed201d8..79d2e4694 100644
--- a/proofs/clenv.ml
+++ b/proofs/clenv.ml
@@ -25,7 +25,6 @@ open Pretype_errors
 open Evarutil
 open Unification
 open Misctypes
-open Sigma.Notations
 
 (******************************************************************)
 (* Clausal environments *)
@@ -337,9 +336,8 @@ let clenv_pose_metas_as_evars clenv dep_mvs =
       else
         let src = evar_source_of_meta mv clenv.evd in
         let src = adjust_meta_source clenv.evd mv src in
-        let evd = Sigma.Unsafe.of_evar_map clenv.evd in
-	let Sigma (evar, evd, _) = new_evar (cl_env clenv) evd ~src ty in
-	let evd = Sigma.to_evar_map evd in
+        let evd = clenv.evd in
+	let (evd, evar) = new_evar (cl_env clenv) evd ~src ty in
 	let clenv = clenv_assign mv evar {clenv with evd=evd} in
 	fold clenv mvs in
   fold clenv dep_mvs
@@ -614,9 +612,7 @@ let make_evar_clause env sigma ?len t =
     | Cast (t, _, _) -> clrec (sigma, holes) n t
     | Prod (na, t1, t2) ->
       let store = Typeclasses.set_resolvable Evd.Store.empty false in
-      let sigma = Sigma.Unsafe.of_evar_map sigma in
-      let Sigma (ev, sigma, _) = new_evar ~store env sigma t1 in
-      let sigma = Sigma.to_evar_map sigma in
+      let (sigma, ev) = new_evar ~store env sigma t1 in
       let dep = not (noccurn sigma 1 t2) in
       let hole = {
         hole_evar = ev;