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/cli/flash.py b/cli/flash.py
index a5af417..aeb48ae 100644
--- a/cli/flash.py
+++ b/cli/flash.py
@@ -144,7 +144,7 @@
     """Thrown when there is an unrecoverable error during flash."""
 
 
-class USBImager(object):
+class USBImager:
     """Copy image to the target removable device."""
 
     def __init__(self, device, board, image, version, debug=False, yes=False):