FCPClientReferenceImplementation: Remove obsolete class.

- SubscriptionSynchronizationHandler was replaced by
BeginSubscriptionSynchronizationHandler and
EndSubscriptionSynchronizationHandler.
- The JavaDoc is mostly recycled at the replacements.
FCPClientReferenceImplementation: Clarify comment
FCPClientReferenceImplementation: Remove overkill JavaDoc

The "Subscribed" reply is what immediately follows the message which
we send here. The other stuff is not a direct reply but rather sent by
WOT as part of the subscription synchronization, which IMHO is out of
scope of the JavaDoc of this function.