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