function scheduler_release(id) {
  var tcb = this.blocks[id];
  if (tcb == null) return tcb;
  tcb_markAsNotHeld.call(tcb);
  if (tcb.priority > this.currentTcb.priority) {
    return tcb;
  } else {
    return this.currentTcb;
  }
}
Release a task that is currently blocked and return the next block to run.
@param {int} id the id of the task to suspend