Steps to reproduce:

1. delete usergroup (no members)

Result:
1. "User group "Test" is used in "Auto-discover: mysql servers" action."

Expected:
Group deleted

Notes:

* "Auto-discover: mysql servers" action is not listed in UI

• it is listed in "action" DB table:

  • # actionid, name, eventsource, evaltype, status, esc_period, formula, pause_suppressed
    '2', 'Auto-discovery: ALL Linux servers', '1', '0', '1', '1h', '', '1'
    '3', 'Report problems to Zabbix administrators', '0', '0', '1', '1h', '', '1'
    '4', 'Report not supported items', '3', '1', '1', '1h', '', '1'
    '5', 'Report not supported low level discovery rules', '3', '0', '1', '1h', '', '1'
    '6', 'Report unknown triggers', '3', '1', '1', '1h', '', '1'
    '7', 'Auto register production hosts', '2', '1', '0', '1h', '', '1'
    '8', 'Auto-discovery: hadoop datanodes', '1', '0', '1', '1h', '', '1'
    '9', 'Alert to Slack', '0', '0', '0', '1h', '', '1'
    '10', 'Auto-discover: bidder nodes', '1', '0', '1', '1h', '', '1'
    '11', 'Auto-discover: mysql servers', '1', '0', '1', '1h', '', '1'