Remove all specified keys from the writer's CHAMP in a single batch operation. Substantially faster than N individual #remove calls.
(WriterData base,
PublicKeyHash owner,
SigningPrivateKeyAndPublicHash sharingKey,
List<Pair<byte[], MaybeMultihash>> keysAndExisting,
TransactionId tid)
source not stored for this graph (policy: none)
no outgoing calls