code: func (db *Database) RemoveUser(user string) error {
  	err := db.Run(bson.D{{"dropUser", user}}, nil)
  	if isNoCmd(err) {
  		users := db.C("system.users")
  		return users.Remove(bson.M{"user": user})
  	}
  	if isNotFound(err) {
  		return ErrNotFound
  	}
  	return err
  }
docs: // RemoveUser removes the authentication credentials of user from the database.