The version in the Pypi JSON is "2.1" but there's no such tag in the
repo and our dep update script does not currently account for such
differences.

The deps update script does not correctly check for compatibility with
Python for direct dependencies of Weblate (such check is only done for
dependencies of dependencies).

Therefore, we manually pin openpyxl version to <3.0 as bigger versions
all depend on Python >= 3.6 which is not available in Debian Stretch.

In its previous location, the dependencies update script was being
served in the Puppet file server, but we don't need that, as such script
is meant to be executed in the admin machine to generate Puppet code.