Remove encoding declaration in Python files (#3568)

As per
https://docs.python.org/3.11/reference/lexical_analysis.html#encoding-declarations,
the default encoding of Python files is UTF-8. In fact, it's been the
default encoding since Python 3.0 (released in 2008).

test/basetest/testing.py

@@ -1,5 +1,3 @@
-# -*- coding: utf-8 -*-
-
 import unittest
 import sys
 from .utils import TASKW_SKIP