Remove type shenanigans from GetListConfigParser
Remove type shenanigans from GetListConfigParser

The stub for RawConfigParser._get_conv has landed in mypy trunk, so we
can remove the casting that was working around its absence.

Also, that stub reveals that getlist shouldn't actually take any
positional arguments in addition to the ones explicitly defined, so
remove them.

OddBloke/jenkins-job-linter