delete Python 2 (object) compat

Bug: 302871152
Change-Id: I39636d73a6e1d69efa8ade74f75c5381651e6dc8
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/390054
Commit-Queue: Mike Frysinger <vapier@google.com>
Reviewed-by: Aravind Vasudevan <aravindvasudev@google.com>
Tested-by: Mike Frysinger <vapier@google.com>

tests/test_git_command.py

@@ -72,7 +72,7 @@ class GitCommandWaitTest(unittest.TestCase):
     """Tests the GitCommand class .Wait()"""
 
     def setUp(self):
-        class MockPopen(object):
+        class MockPopen:
             rc = 0
 
             def __init__(self):