update iris to use stdpp

opam.pins

-coq-iris https://gitlab.mpi-sws.org/FP/iris-coq b0418bd57b9341dbf5e58669c689201daa561bd7
+coq-iris https://gitlab.mpi-sws.org/FP/iris-coq 50a1b62bfaaa3619621b33b0254865e66ecc4fc9

theories/lang/heap.v

 From Coq Require Import Min.
-From iris.prelude Require Import coPset.
+From stdpp Require Import coPset.
 From iris.algebra Require Import cmra_big_op gmap frac agree.
 From iris.algebra Require Import csum excl auth.
 From iris.base_logic Require Import big_op lib.fractional.

theories/lang/lang.v

 From iris.program_logic Require Export language ectx_language ectxi_language.
-From iris.prelude Require Export strings.
-From iris.prelude Require Import gmap.
+From stdpp Require Export strings.
+From stdpp Require Import gmap.
 Set Default Proof Using "Type".
 
 Open Scope Z_scope.

theories/lang/races.v

-From iris.prelude Require Import gmap.
+From stdpp Require Import gmap.
 From iris.program_logic Require Export hoare.
 From iris.program_logic Require Import adequacy.
 From lrust.lang Require Import tactics.

theories/lang/tactics.v

-From iris.prelude Require Import fin_maps.
+From stdpp Require Import fin_maps.
 From lrust.lang Require Export lang.
 Set Default Proof Using "Type".
 

theories/lifetime/lifetime_sig.v

 From iris.algebra Require Import frac.
-From iris.prelude Require Export gmultiset strings.
+From stdpp Require Export gmultiset strings.
 From iris.base_logic.lib Require Export invariants.
 From iris.base_logic.lib Require Import boxes fractional.
 Set Default Proof Using "Type".