always check numcopies when moving from cluster

always check numcopies when moving from cluster

When the destination does not start with a copy, the cluster has one or
more copies. If more, dropping would reduce the number of copies, so
numcopies must be checked.

Considered checking how many nodes of the cluster contain a copy. If
only 1 node does, it could allow a move without checking numcopies.
The problem with that, though, is that other nodes of the cluster could
have copies that we don't know about. And dropping from a cluster tries
to drop from all nodes, so will drop even from those. So any drop from a
cluster can remove more than 1 copy.