Internal: made original indices optional for broadcast delete and delete by query shard requests

Shard requests like broadcast delete and delete by query, that needs to be executed on primary and all replicas, get read and written out to the transport on the same node. That means that if we add some field version checks are not enough to maintain bw comp since a newer node that holds the primary might receive the request from an older node, that didn't provide the field. Yet, when writing the request out again to a newer node that holds the replica, we do try and serialize the field although it's missing. The newer fields just needs to be set to optional in these cases, in addition to the version checks.

Re-enabled testDeleteByQuery and testDeleteRoutingRequired bw comp tests since this was the cause of their failures.