demande-import-test: use `wsgiref` instead of `telnetlib` for testing
The `telnetlib` module has been dropped in 3.13. The `wsgiref` module fit the
same purpose of being obscure and not imported yet.
https://bz.mercurial-scm.org/1089
$ hg init repo
$ cd repo
$ mkdir a
$ echo a > a/b
$ hg ci -Am m
adding a/b
$ hg rm a
removing a/b
$ hg ci -m m a
$ mkdir a b
$ echo a > a/b
$ hg ci -Am m
adding a/b
$ hg rm a
removing a/b
$ cd b
Relative delete:
$ hg ci -m m ../a
$ cd ..