In SERVER-86949 a FixedFCVRegion was added to removeShard in order to prevent dropping the sessions collection on the config server depending on the new feature flag being enabled.

The reasoning for this being ok is that addShard takes a FixedFCV already for a similar period of time. However, the major difference between what addShard does and what removeShard now does is that addShard will fail after acquiring the FixedFCVRegion if we are in a transitional FCV (upgrading or downgrading). This means that addShard can never block leaving the transitional state, only starting an FCV change. Whereas removeShard could block either.

Since there are some known issues with being in the transitional state for a long time, it would be good to minimize the amount of time we spend in that state. So we should reduce the scope of the FixedFCVRegion during removeShard to not contain the ddl blocking which requires contacting all shards.