Formerly, the 'courseware.courseware_mfe' Waffle flag was
required in order use the new Learning-MFE-based courseware
frontend. However, the Learning-MFE-based frontend has since
become the default, with the 'courseware.use_legacy_frontend'
flag instead serving as an opt-out.
The LEARNING_MICROFRONTEND_URL Django setting annotation
erroneously still referenced the old 'courseware.courseware_mfe'
flag. This commit removes the outdated reference.
5b580d2198