Removed deprecated future imports

openedx/core/djangoapps/content/course_overviews/migrations/0018_add_start_end_in_CourseOverview.py

@@ -1,6 +1,6 @@
 # -*- coding: utf-8 -*-
 # Generated by Django 1.11.27 on 2020-01-13 13:55
-from __future__ import unicode_literals
+
 
 from django.db import migrations, models
 

openedx/core/djangoapps/content/course_overviews/migrations/0019_improve_courseoverviewtab.py

@@ -1,9 +1,9 @@
 # -*- coding: utf-8 -*-
 # Generated by Django 1.11.27 on 2020-01-16 17:23
-from __future__ import unicode_literals
 
-from django.db import migrations, models
+
 import django.db.models.deletion
+from django.db import migrations, models
 
 
 class Migration(migrations.Migration):

openedx/core/djangoapps/content/course_overviews/migrations/0020_courseoverviewtab_url_slug.py

@@ -1,6 +1,6 @@
 # -*- coding: utf-8 -*-
 # Generated by Django 1.11.28 on 2020-02-26 15:53
-from __future__ import unicode_literals
+
 
 from django.db import migrations, models