code: @Deprecated
      public WriteResult removeUser(final String userName) {
          try {
              executor.execute(new com.mongodb.operation.DropUserOperation(getName(), userName, getWriteConcern()), getReadConcern());
              return new WriteResult(1, true, null);
          } catch (MongoWriteConcernException e) {
              throw createWriteConcernException(e);
          }
      }
docs: Removes the specified user from the database.
  
  @param userName user to be removed
  @return the result of executing this operation
  @throws MongoException if the operation failed
  @mongodb.driver.manual administration/security-access-control/  Access Control
  @deprecated Use {@code DB.command} to call the dropUser command