Fix __future__ imports, __metaclass__ = type, and remove explicit UTF-8 encoding statement for Python files (#10886)

* Adjust all __future__ imports:

for i in $(grep -REl "__future__.*absolute_import" plugins/ tests/); do
  sed -e 's/from __future__ import .*/from __future__ import annotations/g' -i $i;
done

* Remove all UTF-8 encoding specifications for Python source files:

for i in $(grep -REl '[-][*]- coding: utf-8 -[*]-' plugins/ tests/); do
  sed -e '/^# -\*- coding: utf-8 -\*-/d' -i $i;
done

* Remove __metaclass__ = type:

for i in $(grep -REl '__metaclass__ = type' plugins/ tests/); do
  sed -e '/^__metaclass__ = type/d' -i $i;
done

plugins/connection/chroot.py

@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 # Based on local.py (c) 2012, Michael DeHaan <michael.dehaan@gmail.com>
 #
 # (c) 2013, Maykel Moya <mmoya@speedyrails.com>