Add python to makedeps, add separate dedup stage

Recently upstream has started running check_whence.py prior to the installation process, to ensure the WHENCE metadata is in the correct format.

In addition, the de-duplication stage is no longer forced onto everyone. So anyone interested, can run the separate target.

Both of those are done by yours truly, so direct any rotten tomatoes^W^Wpraise towards me ;-)

Signed-off-by: Emil Velikov emil.l.velikov@gmail.com

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Team, this MR is not tested since I'm not really a Debian person. I'm assuming the idea is obvious enough and the maintainers can take over - commit access to the branch is allowed.

On a somewhat related topic:

• is there particular reason why firmware compression is not enabled? you can easily get 2x (amdgpu) or 3x (iwifi) reduction
• can I offer some virtual 🍪 in exchange for getting the free/redistributable logic in upstream copy-firmware.sh --only=free or alike? ... Gentoo uses a manual list, which could be replaced with your tooling

Happy to swap the virtual 🍪 for an IRL beverage of choice at the next Cambridge Debian (min)conf. I was looking for volunteers at the one we just had alas didn't find any :-)

Thanks o/