Remove the rest of print_function.

frontend_tests/run-casper

@@ -1,5 +1,4 @@
 #!/usr/bin/env python3
-from __future__ import print_function
 import optparse
 import subprocess
 import sys

manage.py

@@ -1,6 +1,5 @@
 #!/usr/bin/env python3
 from __future__ import absolute_import
-from __future__ import print_function
 
 import os
 import sys

zerver/apps.py

@@ -1,4 +1,3 @@
-from __future__ import print_function
 
 from django.apps import AppConfig
 from django.db.models.signals import post_migrate