We remove security patches and custom fixes which are now part of koa.3.
We take the opportunity to make it possible to build the openedx Docker image
without relying on a corresponding openedx-i18n repo tag: often, we want to
test whether the image simply builds successfully, and we don't need up-to-date
translations. For those cases, it's now possible to pass the `-a
OPENEDX_I18N_VERSION=oldertag` build argument.
4a65f24ae7