message: smt expr: remove folding of lambdas
  simplify there is too expensive. saves 1.5 hours per optimization on gcc
  we could replace this with a bounded subst+simpl, but doesnt seem to be worth it
diff: @@ -1708,26 +1708,6 @@ expr expr::load(const expr &idx) const {
  } else if (isConstArray(val)) {
  return val;
  -
  - } else if (Z3_get_ast_kind(ctx(), ast()) == Z3_QUANTIFIER_AST &&
  - Z3_is_lambda(ctx(), ast())) {
  - assert(Z3_get_quantifier_num_bound(ctx(), ast()) == 1);
  - expr body = Z3_get_quantifier_body(ctx(), ast());
  - if (body.isConst())
  - return body;
  -
  - auto subst = [&](const expr &e) {
  - if (e.isLoad(array, str_idx)) {
  - return array.load(str_idx.subst({ idx }));
  - }
  - return e.subst({ idx });
  - };
  -
  - expr cond, then, els;
  - if (body.isIf(cond, then, els)) {
  - cond = cond.subst({ idx }).simplify();
  - return mkIf_fold(cond, subst(then), subst(els));
  - }
  }
  return Z3_mk_select(ctx(), ast(), idx());
  