search-channel: destroy the channels hash table when finalizing
search-channel: destroy the channels hash table when finalizing

That way we don't have to check if the hash table still exist or not.

Ziemin/telepathy-gabble,jku/telepathy-gabble,Ziemin/telepathy-gabble,jku/telepathy-gabble,mlundblad/telepathy-gabble,mlundblad/telepathy-gabble,jku/telepathy-gabble,mlundblad/telepathy-gabble,Ziemin/telepathy-gabble,Ziemin/telepathy-gabble