Fix some style issues.

dulwich/contrib/test_swift.py

@@ -31,7 +31,6 @@ try:
 except ImportError:
     from io import StringIO
 
-import sys
 from unittest import skipIf
 
 from dulwich.tests import (
@@ -40,9 +39,6 @@ from dulwich.tests import (
 from dulwich.tests.test_object_store import (
     ObjectStoreTests,
     )
-from dulwich.tests.utils import (
-    build_pack,
-    )
 from dulwich.objects import (
     Blob,
     Commit,
@@ -50,9 +46,6 @@ from dulwich.objects import (
     Tag,
     parse_timezone,
     )
-from dulwich.pack import (
-    REF_DELTA,
-    )
 
 try:
     from simplejson import dumps as json_dumps

dulwich/diff_tree.py

@@ -19,7 +19,7 @@
 #
 
 """Utilities for diffing files and trees."""
-import sys
+
 from collections import (
     defaultdict,
     namedtuple,

dulwich/fastexport.py

@@ -21,8 +21,6 @@
 
 """Fast export/import functionality."""
 
-import sys
-
 from dulwich.index import (
     commit_tree,
     )

dulwich/hooks.py

@@ -22,7 +22,6 @@
 
 import os
 import subprocess
-import sys
 import tempfile
 
 from dulwich.errors import (

dulwich/objects.py

@@ -27,7 +27,6 @@ from collections import namedtuple
 import os
 import posixpath
 import stat
-import sys
 import warnings
 import zlib
 from hashlib import sha1