In Python 3, the default encoding of source files is utf-8. The encoding
cookie is now unnecessary and redundant so remove it. For more details,
see the docs:
https://docs.python.org/3/howto/unicode.html#the-string-type
> The default encoding for Python source code is UTF-8, so you can
> simply include a Unicode character in a string literal ...
Includes a fix for the flake8 header checks to stop expecting an
encoding cookie.
We noticed this issue with the 0.2.x release of snide/sphinx_rtd_theme. Because
we are calling toctree unconditionally, we notice a bug in the singlehtml
builder when the docs have an empty/nonexistant toctree. In this case,
`fix_refuris` as being passed `None`, which failed to traverse, throwing an
exception.
This conditionally fixes the refuris instead.
