Deprecate eventbus, async-eventbus and fixed-threadpool

I've done a grep on their namespace in autorelease, and I can see that no-one is using those module:

Namespace tied to async-eventbus and eventbus: urn:opendaylight:params:xml:ns:yang:controller:threadpool:impl
That one is used only to leverage "threadfactory-naming" module.

Namespace tied to fixed-threadpool:
urn:opendaylight:params:xml:ns:yang:controller:threadpool:impl:fixed