Remove incompatible SSL option in Python 2.6

An exposed SSL option, `ciphers`, was added in Python 2.7 and breaks older
versions of Python with an unexpected kwargs error.

I'm not sure if this is the best way to fix this, and I'm happy to consider
other approachs. Here are some thoughts I had:

  i) Explicit failure is a hard requirement.

  ii) Meaninful config values shouldn't ever be `None`.