Remove AuthenticationError, ExportError, FetchError.

signac/common/errors.py

@@ -9,28 +9,3 @@ class ConfigError(Error, RuntimeError):
     """Error with parsing or reading a configuration file."""
 
     pass
-
-
-# this class is only used by deprecated features
-class AuthenticationError(Error, RuntimeError):
-    """Authentication error."""
-
-    def __str__(self):
-        if len(self.args) > 0:
-            return f"Failed to authenticate with host '{self.args[0]}'."
-        else:
-            return "Failed to authenticate with host."
-
-
-# this class is only used by deprecated features
-class ExportError(Error, RuntimeError):
-    """Error exporting documents to a mirror."""
-
-    pass
-
-
-# this class is only used by deprecated features
-class FetchError(FileNotFoundError):
-    """Error in fetching data."""
-
-    pass