Revert remains of 'upgrade upsell to course info banner'.

TNL-6381 added an upgrade upsell to course info. In PR #15265, this was
partially removed/moved, but some clean-up work remained.

LEARNER-2026

lms/djangoapps/courseware/views/views.py

@@ -30,7 +30,6 @@ from courseware.courses import (
     sort_by_announcement,
     sort_by_start_date
 )
-from courseware.date_summary import VerifiedUpgradeDeadlineDate
 from courseware.masquerade import setup_masquerade
 from courseware.model_data import FieldDataCache
 from courseware.models import BaseStudentModuleHistory, StudentModule
@@ -404,9 +403,6 @@ def course_info(request, course_id):
         return render_to_response('courseware/info.html', context)
 
 
-UPGRADE_COOKIE_NAME = 'show_upgrade_notification'
-
-
 class StaticCourseTabView(EdxFragmentView):
     """
     View that displays a static course tab with a given name.