You can use an ‘inferior’[0] Guix if you don't
mind the entire closure of python2-flask* being
frozen in the past -- possibly including
incompatibilities or known security
vulnerabilities.
I don't know what their inclusion & maintenance
criteria are, but another approach is to add the
removed packages to the guix-past[1] channel.
I reckon using guix-past (or another channel)
would be the way to go. I can't see any packages
that use "inferiors" yet; when that happens, it'd
be a good idea to start considering it!