eventpluginsmanager: don't crash on double-delete of plugin objects
The Qt docs command no deletes!
Don't try to delete the root component. Instead rely on that unload() will automatically delete it when needed.
and
When the library is finally unloaded, the root component will automatically be deleted.
consequently don't delete the root component and then crash when a double delete occurs. This notably seems easy to produce with multiple clocks that have events plugins loaded.