flake8, more frozen

src/allmydata/cli/grid_manager.py

@@ -4,7 +4,6 @@ A CLI for configuring a grid manager.
 
 from typing import Optional
 from datetime import (
-    datetime,
     timedelta,
 )
 

src/allmydata/grid_manager.py

@@ -25,9 +25,7 @@ from allmydata.util import (
 )
 
 from attrs import (
-    define,
     frozen,
-    asdict,
     Factory,
 )
 
@@ -93,7 +91,7 @@ class _GridManagerStorageServer(object):
         }
 
 
-@define
+@frozen
 class _GridManagerCertificate(object):
     """
     Represents a single certificate for a single storage-server

src/allmydata/test/test_grid_manager.py

@@ -22,7 +22,6 @@ from allmydata.crypto import (
     ed25519,
 )
 from allmydata.util import (
-    base32,
     jsonbytes as json,
 )
 from allmydata.grid_manager import (