Refs #23919 -- Removed Python 2 notes in docs.

docs/intro/contributing.txt

@@ -70,9 +70,9 @@ probably got the answers.
 
 .. admonition:: Python 3 required!
 
-    This tutorial assumes you are using Python 3. Get the latest version at
-    `Python's download page <https://www.python.org/download/>`_ or with your
-    operating system's package manager.
+    The current development version of Django doesn't support Python 2.7. Get
+    Python 3 at `Python's download page <https://www.python.org/download/>`_ or
+    with your operating system's package manager.
 
 .. admonition:: For Windows users
 

docs/intro/overview.txt

@@ -33,7 +33,7 @@ database-schema problems. Here's a quick example:
     class Reporter(models.Model):
         full_name = models.CharField(max_length=70)
 
-        def __str__(self):              # __unicode__ on Python 2
+        def __str__(self):
             return self.full_name
 
     class Article(models.Model):
@@ -42,7 +42,7 @@ database-schema problems. Here's a quick example:
         content = models.TextField()
         reporter = models.ForeignKey(Reporter, on_delete=models.CASCADE)
 
-        def __str__(self):              # __unicode__ on Python 2
+        def __str__(self):
             return self.headline
 
 Install it

docs/intro/reusable-apps.txt

@@ -220,10 +220,8 @@ this. For a small app like polls, this process isn't too difficult.
                'License :: OSI Approved :: BSD License',  # example license
                'Operating System :: OS Independent',
                'Programming Language :: Python',
-               # Replace these appropriately if you are stuck on Python 2.
-               'Programming Language :: Python :: 3',
-               'Programming Language :: Python :: 3.4',
                'Programming Language :: Python :: 3.5',
+               'Programming Language :: Python :: 3.6',
                'Topic :: Internet :: WWW/HTTP',
                'Topic :: Internet :: WWW/HTTP :: Dynamic Content',
            ],