Bug#936456: dune-common: Python2 removal in sid/bullseye

[Ansgar]

Control: tag -1 + confirmed

Matthias Klose writes:
> Your package either build-depends, depends on Python2, or uses Python2
> in the autopkg tests.  Please stop using Python2, and fix this issue
> by one of the following actions.

python2 is only used for a script that helps with migrating DUNE modules
from its old autotools buildsystem to CMake.  I don't think it is worth
porting it to python3 and will likely remove it from the Debian package
with the next upload; maybe it should also be removed upstream.

Ansgar