code: function(key) {
          this._removeAddsOrRemoves(this.sets.adds, key);
          this._removeAddsOrRemoves(this.sets.removes, key);
          if (this.sets.remove.indexOf(key) === -1) {
              this.sets.remove.push(key);
          }
          return this;
      }
docs: Remove a set from a map.
  @method removeSet
  @param {String} key the key for the set in the map.
  @chainable