code: function removeOverlapPoints(points) {
              var hash = {};
              var ret = [];
              for (var i = 0, l = points.length; i < l; i++) {
                  var hashcode = points[i].x * 31 + points[i].y;
                  if (!hash[hashcode]) {
                      ret.push(points[i]);
                      hash[hashcode] = 1;
                  }
              }
              return ret;
          }
docs: 移除重复点
  
  @param {Array} points 点集合
  @return {Array} 移除后点集合