public void removeAlertDefinition(AlertDefinitionEntity definition) {
    if (null != alertDefinitions) {
      alertDefinitions.remove(definition);
    }

    definition.removeAlertGroup(this);
  }
Removes the specified definition from the definitions that this group will
dispatch to.

@param definition
         the definition to remove (not {@code null}).
ambari-server/src/main/java/org/apache/ambari/server/orm/entities/AlertGroupEntity.java