CMML: do not (ab)use the interface subsystem

CMML: do not (ab)use the interface subsystem

Only the core can safely destroy an interface, otherwise, the other
component could race against the core in joining the interface thread
or destroying the interface object.
The fire and forget status of interfaces is by design, and is expected
by -at least- the VLC binary, the NT service plugin and the Remote
Control interface plugin. Anyway, that is pretty the only point of
creating an interface instead of a private thread/object.