[NFC] Remove Python 2 imports from __future__ (#42086)

The `__future__` we relied on is now,  where the 3 specific things are
all included [since Python 3.0](https://docs.python.org/3/library/__future__.html):

* absolute_import
* print_function
* unicode_literals
* division

These import statements are no-ops and are no longer necessary.

utils/python_lint.py

@@ -16,8 +16,6 @@ sources.
 """
 
 
-from __future__ import absolute_import, print_function, unicode_literals
-
 import os
 import subprocess
 import sys