Remove outdated assertions.

This code should have been removed when Datasets no longer set up
their dataset packages (DM-12853).

tests/test_dataset.py

@@ -58,11 +58,6 @@ def testDatasets(self):
         datasets = Dataset.getSupportedDatasets()
         self.assertIn(DatasetTestSuite.datasetKey, datasets)  # assumed by other tests
 
-        # Initializing another Dataset has side effects, alas, but should not
-        # invalidate tests of whether ap_verify_testdata has been loaded
-        for dataset in datasets:
-            Dataset(dataset)
-
     def testDirectories(self):
         """Verify that a Dataset reports the desired directory structure.
         """