Fix and reenable useless-object-inheritance.

Initial change generated using:
git ls-tree -r HEAD | awk '$1 != "120000" {print $NF}' | \
  grep '\.py$' | grep -v -e ^third_party/ -e '_pb2\.py' | \
  xargs sed -i 's/(object)//g'

Required only a handful of manual edits after that, mostly for
unrelated lint fixes.

BUG=None
TEST=run_tests, CQ

Change-Id: I0c57fdcf20124530ecd33ae3118506a2be9fc0ed
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/4637436
Auto-Submit: Alex Klein <saklein@chromium.org>
Commit-Queue: Jack Rosenthal <jrosenth@chromium.org>
Tested-by: Alex Klein <saklein@chromium.org>
Reviewed-by: Jack Rosenthal <jrosenth@chromium.org>
diff --git a/scripts/gconv_strip_unittest.py b/scripts/gconv_strip_unittest.py
index 4b1831b..4d4048b 100644
--- a/scripts/gconv_strip_unittest.py
+++ b/scripts/gconv_strip_unittest.py
@@ -59,7 +59,7 @@
         )
         self.PatchObject(gconv_strip.lddtree, "ParseELF", return_value={})
 
-        class _StubStat(object):
+        class _StubStat:
             """Fake for lstat."""
 
             st_size = 0