Add missing python_version=2 to packages the require it

[ahesford]

This fixes #21323, where packages use pycompile_dirs without declaring python_version or installing packages to /usr/lib/pythonX.Y to allow automatic detection of the Python version.

Adding the python_version (and a few xlint fixes) will not change the build outputs, so I have not revbumped these templates and am skipping CI.

[Chocimier]

Some are python3, e.g. hugin, soundconverter.

[ahesford]

I forgot to add the #unverified comment, but have added it in the latest push. The point is not to get the correct version in all of these packages, but to restore the default behavior to allow these packages to build as before the behavior change. I don't have the resources to check all packages at the moment.

Because you know hugin and soundconverter are py3, I've updated those packages. I've also noticed that qytdl pulls in py3 depenedents, so I've updated that template as well. The gdb package uses version-agnostic python modules, but the template specifies python3 dependencies so I've changed that one too.