code: function (observer, property) {
          if (!property)
              property = ALL;
          var arr = this.props[property];
          if (arr) {
              for (var i = 0, sz = arr.length; sz > i; i++) {
                  if (arr[i] === observer) {
                      arr.splice(i, 1);
                      sz -= 1;
                      i -= 1;
                  }
              }
              if (arr.length === 0) {
                  this.props[property]=null;
              }
          }
      }
docs: Remove an observer - previously added with addObserver()
  @param {object} observer object with a onPropChange() method
  @param {string} property the property name to observe (optional)