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.

This is consistent with "Complete Table of Contents" (which is already
in the database), as well as e.g. "Indices and Tables" where "and" is
not capitalized.

This is also fairly standard title-case practice.