Clearing the cache if the site's configuration was removed.

The site's configuration does not contain the API URL, it should not keep on displayed the old cached list of uuids.
LEARNER-1146

openedx/core/djangoapps/catalog/management/commands/cache_programs.py

@@ -50,6 +50,7 @@ class Command(BaseCommand):
                 site_config = getattr(site, 'configuration', None)
                 if site_config is None or not site_config.get_value('COURSE_CATALOG_API_URL'):
                     logger.info('Skipping site {domain}. No configuration.'.format(domain=site.domain))
+                    cache.set(SITE_PROGRAM_UUIDS_CACHE_KEY_TPL.format(domain=site.domain), [], None)
                     continue
 
                 client = create_catalog_api_client(user, site=site)