Improve CourseListView end point latency by removing CourseWaffleFlag.

This patch would remove CourseListView slow transaction by changing
CourseWaffleFlag to WaffleFlag. This removes extra hit on
WaffleUtil's model (WaffleFlagCourseOverrideModel).

LEARNER-5566

lms/djangoapps/courseware/access_utils.py

@@ -91,6 +91,6 @@ def check_course_open_for_learner(user, course):
     Returns:
         AccessResponse: Either ACCESS_GRANTED or StartDateError.
     """
-    if COURSE_PRE_START_ACCESS_FLAG.is_enabled(course.id):
+    if COURSE_PRE_START_ACCESS_FLAG.is_enabled():
         return ACCESS_GRANTED
     return check_start_date(user, course.days_early_for_beta, course.start, course.id)

openedx/features/course_experience/__init__.py

@@ -4,7 +4,7 @@ Unified course experience settings and helper methods.
 from django.utils.translation import ugettext as _
 
 from openedx.core.djangoapps.util.user_messages import UserMessageCollection
-from openedx.core.djangoapps.waffle_utils import CourseWaffleFlag, WaffleFlagNamespace
+from openedx.core.djangoapps.waffle_utils import CourseWaffleFlag, WaffleFlagNamespace, WaffleFlag
 
 
 # Namespace for course experience waffle flags.
@@ -20,7 +20,7 @@ UNIFIED_COURSE_TAB_FLAG = CourseWaffleFlag(WAFFLE_FLAG_NAMESPACE, 'unified_cours
 DISPLAY_COURSE_SOCK_FLAG = CourseWaffleFlag(WAFFLE_FLAG_NAMESPACE, 'display_course_sock')
 
 # Waffle flag to let learners access a course before its start date.
-COURSE_PRE_START_ACCESS_FLAG = CourseWaffleFlag(WAFFLE_FLAG_NAMESPACE, 'pre_start_access')
+COURSE_PRE_START_ACCESS_FLAG = WaffleFlag(WAFFLE_FLAG_NAMESPACE, 'pre_start_access')
 
 # Waffle flag to enable a review page link from the unified home page.
 SHOW_REVIEWS_TOOL_FLAG = CourseWaffleFlag(WAFFLE_FLAG_NAMESPACE, 'show_reviews_tool')