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>

command.py

@@ -46,7 +46,7 @@ class UsageError(RepoExitError):
     """Exception thrown with invalid command usage."""
 
 
-class Command(object):
+class Command:
     """Base class for any command line action in repo."""
 
     # Singleton for all commands to track overall repo command execution and
@@ -498,11 +498,11 @@ class PagedCommand(Command):
         return True
 
 
-class MirrorSafeCommand(object):
+class MirrorSafeCommand:
     """Command permits itself to run within a mirror, and does not require a
     working directory.
     """
 
 
-class GitcClientCommand(object):
+class GitcClientCommand:
     """Command that requires the local client to be a GITC client."""