kDropping isn't needed. Here's why:

1. On shards that are only donors, they can instead drop on kRenaming.
2. On shards that are donors and recipients, the drop happens as part of the local rename operation.

As part of this ticket, it's reasonable to assume that kDropping on the donor should be replaced with kRenaming. As part of this ticket, assess if that makes sense, and take action based on the assessment.

This ticket must be done before SERVER-52801. SERVER-52801 will handle the local dropping with donor-only shards and intra-shard synchronization with shards that are both donors and recipients.