feat!: Drop the legacy files and uplades page.

The assets page and related tests and settings flags will be removed.
They have been replaced with a new implementation in the
frontend-app-authoring MFE.

BREAKING CHANGE: The legacy_studio.files_uploads flag has been removed
and will no longer allow operators to fall back to the legacy files and
uploads view.  The new MFE version is now the only available veiew.

cms/templates/widgets/header.html

@@ -47,7 +47,6 @@
             checklists_url = reverse('checklists_handler', kwargs={'course_key_string': str(course_key)})
             pages_and_resources_mfe_enabled = ENABLE_PAGES_AND_RESOURCES_MICROFRONTEND.is_enabled(context_course.id)
             updates_mfe_enabled = toggles.use_new_updates_page(context_course.id)
-            files_uploads_mfe_enabled = toggles.use_new_files_uploads_page(context_course.id)
             video_upload_mfe_enabled = toggles.use_new_video_uploads_page(context_course.id)
             schedule_details_mfe_enabled = toggles.use_new_schedule_details_page(context_course.id)
             grading_mfe_enabled = toggles.use_new_grading_page(context_course.id)
@@ -104,16 +103,9 @@
                     <a href="${get_pages_and_resources_url(course_key)}">${_("Pages & Resources")}</a>
                   </li>
                   % endif
-                  %if not files_uploads_mfe_enabled:
-                  <li class="nav-item nav-course-courseware-uploads">
-                    <a href="${assets_url}">${_("Files")}</a>
-                  </li>
-                  %endif
-                  %if files_uploads_mfe_enabled:
                   <li class="nav-item nav-course-courseware-uploads">
                     <a href="${get_files_uploads_url(course_key)}">${_("Files")}</a>
                   </li>
-                  %endif
                   % if not pages_and_resources_mfe_enabled:
                   <li class="nav-item nav-course-courseware-textbooks">
                     <a href="${textbooks_url}">${_("Textbooks")}</a>