Remove deprecated Python utf8 encoding declaration

[cclauss]

% ruff rule UP009

utf8-encoding-declaration (UP009)

Derived from the pyupgrade linter.

Fix is always available.

What it does

Checks for unnecessary UTF-8 encoding declarations.

Why is this bad?

PEP 3120 makes UTF-8 the default encoding, so a UTF-8 encoding
declaration is unnecessary.

Example

# -*- coding: utf-8 -*-
print("Hello, world!")

Use instead:

print("Hello, world!")