[willow] Remove legacy library CMS view handlers

[salman2013]

Parent issue

Part of #38056

Context

cms/djangoapps/contentstore/views/library.py (~352 lines) implements all V1 library views. With the listing already removed (#37454), the remaining views (create, edit, user-access, import, export) can be removed.

Files to modify

• cms/djangoapps/contentstore/views/library.py — delete or gut the file
• cms/djangoapps/contentstore/views/__init__.py — remove any imports
• cms/djangoapps/contentstore/views/tests/test_library.py — delete

Approach

1. Remove functions: library_handler, manage_library_users, _create_library, _display_library, _list_libraries, library_blocks_view
2. Keep any functions required by migration endpoints if still referenced
3. Delete accompanying test file
4. Run: pytest cms/djangoapps/contentstore/ to confirm no regressions

Acceptance criteria

No library_handler or manage_library_users routes return anything; their URL patterns return 404 or are removed.