debian: replace clean with override_dh_auto_clean The current version does not call the default dh_auto_build, which is a bug. This is required in particular for cleaning the build directories.

debian: replace build line with a override_dh_auto_build line This is more in line with how dh is supposed to work. In particular, dh_auto_build is functionally equivalent to the repeated "dh build --with python2 --buildsystem=python_distutils" used currently.