Removed outdated Python 2 references from contributing docs.

Author: nessita

docs/internals/contributing/writing-code/coding-style.txt

@@ -170,7 +170,7 @@ Imports
       :caption: ``django/contrib/admin/example.py``
 
       # future
-      from __future__ import unicode_literals
+      from __future__ import annotations
 
       # standard library
       import json

docs/intro/contributing.txt

@@ -71,12 +71,6 @@ It contains lots of great information and is a must-read for anyone who'd like
 to become a regular contributor to Django. If you've got questions, it's
 probably got the answers.
 
-.. admonition:: Python 3 required!
-
-    The current version of Django doesn't support Python 2.7. Get Python 3 at
-    `Python's download page <https://www.python.org/downloads/>`_ or with your
-    operating system's package manager.
-
 .. admonition:: For Windows users
 
     See :ref:`install_python_windows` on Windows docs for additional guidance.