The bulk of the dropCollection business logic currently sits in a function on the ShardingCatalogClient.

As part of moving the dropCollection command to the config server, we should move the business logic from the ShardingCatalogClient to the ShardingCatalogManager.

Note, the ShardingCatalogClient hierarchy is:
ShardingCatalogClient base class
--> child class ShardingCatalogClientImpl (the real implemenation)
--> child class ShardingCatalogClientMock (has dummy methods)

Moving the dropCollection function will require deleting code from all three of these classes.

Also note, moving the dropCollection function will also require updating some unit tests.