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/exceptions.py

@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 import signal
 
 sig_names = dict((k, v) for v, k in reversed(sorted(signal.__dict__.items()))