Context
Tracking unsharded collections upon creations is for now suspended and won't make it for 9.0. An effort to remove the feature flag while still maintaining proper coverage for tracked collection is document in SERVER-98504. 

Problem
AddShard registers as unsharded all the new collections found in the added replica set.

In case we track upon creation, those collections should be registered in the global catalog.
That logic has been untested for a while as the feature flag is fully disabled, and after SERVER-98504 will be removed, which makes this code unnecessary.

The logic is expressed in addShardInTransaction which should be modified to consider the list of collections to track as always empty.