Ok, i think we can put an end to this thread. As the commands say's, it has just stop/start/status.. Doesn't have a delete option. so this is expected.
As i told earlier, deleting from console will be available in 11g.
A last resort to your problemcould be to delete the blackouts.xml file located in $AGENT_HOME\sysman\emd. This is is not a recommendation, just an observation, please contact oracle support for their supported procedure!