Refs #23919 -- Removed encoding preambles and future imports

docs/ref/files/file.txt

@@ -111,7 +111,6 @@ The ``ContentFile`` class
     but unlike :class:`~django.core.files.File` it operates on string content
     (bytes also supported), rather than an actual file. For example::
 
-        from __future__ import unicode_literals
         from django.core.files.base import ContentFile
 
         f1 = ContentFile("esta sentencia está en español")

docs/ref/migration-operations.txt

@@ -310,9 +310,6 @@ class in the migration file, and just pass it to ``RunPython``. Here's an
 example of using ``RunPython`` to create some initial objects on a ``Country``
 model::
 
-    # -*- coding: utf-8 -*-
-    from __future__ import unicode_literals
-
     from django.db import migrations, models
 
     def forwards_func(apps, schema_editor):