refactor: remove ENABLE_HOME_PAGE_COURSE_API_V2 feature toggle

[BryanttV]

Description

This PR removes the ENABLE_HOME_PAGE_COURSE_API_V2 feature toggle and all its related code. With this change, the API v2 will always be available.

Other Changes

Since the feature toggle was removed, as well as API v2, API v1 will obtain the courses summary from the CourseOverview.get_all_courses()

Testing instructions

1. Create a Tutor environment.

2. Create a mount of edx-platform with the changes in this branch.

3. Consume the endpoints of HomePageCourseAPI:

   API v2

   http://studio.local.openedx.io:8001/api/contentstore/v2/home/courses
   

   API v1

   http://studio.local.openedx.io:8001/api/contentstore/v1/home/courses
   

4. You should see the endpoint responses without any problem.

Deadline

None

Other information

None

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