Remove no-op __future__ imports, Unicode strings

[DavidCain]

Version 2.3 officially dropped support for Python 2.7 (which reached its end of life at the end of 2020).

In Python 3, all string literals are Unicode.

Expressly stating file encoding (with # -*- coding: utf-8 -*-) is no longer necessary (files now default to being interpreted as UTF-8 instead of ASCII), but it's somewhat harmless.