Currently dropIndex only runs on shards that own chunks for the input namespace.

This can cause an issue because we might miss an index if a background migration drains a shard right before running the drop

The perfect solution would be to clean from the shard any residual metadata after a shard is drained.

For now, as implemented for SERVER-71819  a good approach can be

• run dropIndex on every shard that own chunks and ensure the response is OK
• run dropIndex on every shard that DOESN'T own a chunk and ignore the response (best effort)

This will mitigate (but not solve) the issue