Revert 642ab8ec; ref #3422

Also fix #3499.  The issue was solved by #3462.

src/vm.c

@@ -289,7 +289,6 @@ ecall(mrb_state *mrb, int i)
   mrb_value *self = mrb->c->stack;
   struct RObject *exc;
   int cioff;
-  ptrdiff_t nstk;
 
   if (i<0) return;
   if (mrb->c->ci - mrb->c->cibase > MRB_FUNCALL_DEPTH_MAX) {
@@ -301,7 +300,6 @@ ecall(mrb_state *mrb, int i)
     mrb->c->ci->eidx = i;
   cioff = mrb->c->ci - mrb->c->cibase;
   ci = cipush(mrb);
-  nstk = ci->stackent - mrb->c->stbase;
   ci->stackent = mrb->c->stack;
   ci->mid = ci[-1].mid;
   ci->acc = CI_ACC_SKIP;
@@ -313,7 +311,6 @@ ecall(mrb_state *mrb, int i)
   exc = mrb->exc; mrb->exc = 0;
   mrb_run(mrb, p, *self);
   mrb->c->ensure[i] = NULL;
-  ci->stackent = mrb->c->stbase + nstk;
   mrb->c->ci = mrb->c->cibase + cioff;
   if (!mrb->exc) mrb->exc = exc;
 }