fix: remove redundant code from unregister_dataset

get_dataset() will raise an exception if a dataset
won't be returned

client handling is redundant

Signed-off-by: Nathan Weinberg <nweinber@redhat.com>

llama_stack/distribution/routing_tables/datasets.py

@@ -88,6 +88,4 @@ class DatasetsRoutingTable(CommonRoutingTableImpl, Datasets):
 
     async def unregister_dataset(self, dataset_id: str) -> None:
         dataset = await self.get_dataset(dataset_id)
-        if dataset is None:
-            raise DatasetNotFoundError(dataset_id)
         await self.unregister_object(dataset)