Make implementation-centric docstring into a comment.

DO NOT MERGE; SQUASH.

python/lsst/daf/butler/queries/_query.py

@@ -98,12 +98,12 @@ def constraint_dataset_types(self) -> Set[str]:
         The existence of datasets of these types constrains the data IDs of any
         type of result.  Fields for these dataset types are also usable in
         'where' expressions.
-
-        Note that this includes only dataset type names, not `DatasetType`
-        instances; the `DatasetQueryResults` adapter returned by the `datasets`
-        method does include `DatasetType` instances, since it is in a better
-        position to track and respect any storage class override specified.
         """
+        # Note that this includes only dataset type names, not `DatasetType`
+        # instances; the `DatasetQueryResults` adapter returned by the
+        # `datasets` method does include `DatasetType` instances, since it is
+        # in a better position to track and respect any storage class override
+        # specified.
         return self._tree.datasets.keys()
 
     @property