feat: Convert contentserver to view permanently (drop middleware and …

…flag) (#35420)

Final planned portion of #34702 -- waffle flag and middleware are removed.

Commits:

1. Feature change
    - Delete `content_server.use_view` waffle flag in favor of always using view
    - Delete the husk of `StaticContentServerMiddleware` and references to it
    - Update views module docstring
2. Refactor (move)
    - Move contentserver implementation into views.py
3. Lint cleanup
    - Fix import ordering (from refactor debris + amnestied lint)

cms/envs/common.py

@@ -949,7 +949,6 @@
     'openedx.core.djangoapps.cache_toolbox.middleware.CacheBackedAuthenticationMiddleware',
 
     'common.djangoapps.student.middleware.UserStandingMiddleware',
-    'openedx.core.djangoapps.contentserver.middleware.StaticContentServerMiddleware',
 
     'django.contrib.messages.middleware.MessageMiddleware',
     'common.djangoapps.track.middleware.TrackMiddleware',

lms/envs/common.py

@@ -2295,7 +2295,6 @@ def _make_locale_paths(settings):  # pylint: disable=missing-function-docstring
     'openedx.core.djangoapps.safe_sessions.middleware.EmailChangeMiddleware',
 
     'common.djangoapps.student.middleware.UserStandingMiddleware',
-    'openedx.core.djangoapps.contentserver.middleware.StaticContentServerMiddleware',
 
     # Adds user tags to tracking events
     # Must go before TrackMiddleware, to get the context set up