feat!: Remove the django-splash app.

DEPR: https://github.com/openedx/public-engineering/issues/224

The django-splash repo was created 11 years ago to let the LMS redirect
users to a splash screen when a user comes to the site for the first
time. It works by looking for a configurable cookie value and
redirecting from the middleware.

This feature was never documented, has some edx.org hardcoded defaults,
and is not compatible with MFEs.

BREAKING CHANGE: The django splash feature will no longer be available.

lms/envs/common.py

@@ -2286,8 +2286,6 @@ MIDDLEWARE = [
     'openedx.core.djangoapps.cors_csrf.middleware.CorsCSRFMiddleware',
     'openedx.core.djangoapps.cors_csrf.middleware.CsrfCrossDomainCookieMiddleware',
 
-    'splash.middleware.SplashMiddleware',
-
     'openedx.core.djangoapps.geoinfo.middleware.CountryMiddleware',
     'openedx.core.djangoapps.embargo.middleware.EmbargoMiddleware',
 
@@ -3162,9 +3160,6 @@ INSTALLED_APPS = [
     # Notes
     'lms.djangoapps.edxnotes',
 
-    # Splash screen
-    'splash',
-
     # User API
     'rest_framework',
 

requirements/edx/kernel.in

@@ -51,7 +51,6 @@ django-pipeline
 django-ratelimit
 django-sekizai
 django-simple-history
-django-splash
 django-statici18n
 django-storages
 django-user-tasks