Werk #11484: Management Board: Remove explicit check plugins

The only difference of check plugins for Management Boards was the resulting service description. In case, the plugin was related to a Management Board, the prefix "Management Interface:" was set by the check plugin.

As the discovery now handles this scenario, the explicit check plugins are not needed any more.

Note: If you use local checks that use plugin sections that have an equivalent Management Board section, changes on that checks also affect the processing of the Management Board plugin section, e.g. <<<snmp_info>>> on <<<mgmt_snmp_info>>>.

To the list of all Werks