function stackDelete(key) {
  var data = this.__data__,
      result = data['delete'](key);

  this.size = data.size;
  return result;
}
Removes `key` and its value from the stack.

@private
@name delete
@memberOf Stack
@param {string} key The key of the value to remove.
@returns {boolean} Returns `true` if the entry was removed, else `false`.