Remove unnecessary directory check at startup

* Loading root.json will fail just as descriptively
* As long as Bundle doesn't implement bootstrapping
  the local repo, there's also no need to create
  missing directories

Signed-off-by: Jussi Kukkonen <jkukkonen@vmware.com>

tuf/client_rework/metadata_bundle.py

@@ -134,10 +134,6 @@ def __init__(self, repository_path: str):
         self._bundle = {}  # type: Dict[str: Metadata]
         self.reference_time = None
 
-        if not os.path.exists(self._path):
-            # TODO try to create dir instead?
-            raise exceptions.RepositoryError("Repository does not exist")
-
         # Load and validate the local root metadata
         # Valid root metadata is required
         logger.debug("Loading local root")