Drop or refactor FauxFactory warnings

Drop the class-wide FauxFactory deprecation warning, as it is often emitted
unnecessarily. This warning is emitted whenever the class is defined, and the
class is defined whenever the fauxfactory module is imported.

Refactor the `deprecated` decorator function. Make it comply with pylint and
flake8, drop a single-use variable, etc.
Merge pull request #61 from Ichimonji10/fauxfactory-warn

Drop or refactor FauxFactory warnings