Removed dead code

[movermeyer]

Unless I'm mistaken, there is no way that value can be an instance of ConfigList or ConfigTree.

ConfigList is a subclass of list, ConfigTree is a subclass of OrderedDict. There are no assignments to os.environ, nor can these types be assigned to os.environ anyway.

See http://stackoverflow.com/questions/39949587/can-python-os-environ-get-ever-return-a-non-string for a discussion.

[coveralls]

Coverage increased (+0.1%) to 97.636% when pulling c0dba4f99a12c7148cce20629f9f2b1fa3171c60 on movermeyer:patch-2 into 8ea07ebad37d1386ef6f43b8b944f8a56f5ae5ab on chimpler:master.

[movermeyer]

cc @darthbear