code: function(joint){
          var remove=joint;
          var prev=remove.prev;
          var next=remove.next;
          if(prev!==null)prev.next=next;
          if(next!==null)next.prev=prev;
          if(this.joints==remove)this.joints=next;
          remove.prev=null;
          remove.next=null;
          this.numJoints--;
          remove.awake();
          remove.detach();
          remove.parent=null;
      }
docs: I will remove the joint from the world.
  Joint that has been added will be the operands of each step.
  @param  shape Joint to be deleted