Take out configure_payments hack

With the upgrade to the balanced library in #2036 we no longer need this
workaround for https://github.com/balanced/balanced-python/issues/5.
Removing at this point because I'm ripping out all of our direct
os.environ usage and this applies.
Merge pull request #2232 from gittip/un-configure_payments

Take out configure_payments hack
Remove os.environ from wireup.billing