patman: fix pep8 warnings in settings module

Remove extraneous imports, variables and comply to PEP 8 maximum line
width, among other PEP 8 changes suggested by Pyflake.

Signed-off-by: Maxim Cournoyer <maxim.cournoyer@savoirfairelinux.com>
Reviewed-by: Simon Glass <sjg@chromium.org>