Remove encoding cookie from Python source files

Unnecessary since dropping Python 2. Python now decodes files as utf-8
by default.

docs/html/conf.py

@@ -1,5 +1,3 @@
-# -*- coding: utf-8 -*-
-#
 # pip documentation build configuration file, created by
 # sphinx-quickstart on Tue Apr 22 22:08:49 2008
 #

src/pip/_internal/commands/wheel.py

@@ -1,5 +1,3 @@
-# -*- coding: utf-8 -*-
-
 import logging
 import os
 import shutil

tests/functional/test_install_wheel.py

@@ -1,5 +1,3 @@
-# -*- coding: utf-8 -*-
-
 import csv
 import distutils
 import glob

tests/lib/path.py

@@ -1,5 +1,4 @@
 # flake8: noqa
-# -*- coding: utf-8 -*-
 # Author: Aziz Köksal
 import glob
 import os

tests/unit/test_compat.py

@@ -1,5 +1,3 @@
-# -*- coding: utf-8 -*-
-
 import locale
 import os
 import sys

tests/unit/test_utils.py

@@ -1,5 +1,3 @@
-# -*- coding: utf-8 -*-
-
 """
 util tests
 

tests/unit/test_utils_subprocess.py

@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 import locale
 import sys
 from logging import DEBUG, ERROR, INFO, WARNING

tests/unit/test_wheel.py

@@ -1,5 +1,3 @@
-# -*- coding: utf-8 -*-
-
 """Tests for wheel binary packages and .dist-info."""
 import csv
 import logging