Purges the server plugin from the database. This ensures that, after this method returns, the given plugin will be unknown. The plugin can be installed again later. This has "requires new" semantics, so the results are committed immediately upon return.
Do not invoke this method directly. It is meant as a support for {@link org.rhq.enterprise.server.scheduler.jobs.PurgePluginsJob}.
@param pluginId the id of the server plugin to delete