Consider deleting verification-extension.git and ~"C:Verification Extension" label

Now that we have tails#16128, we don't need https://gitlab.tails.boum.org/tails/verification-extension anymore.

I'm not sure what's your policy regarding unused repos but feel free to delete it if it makes sense.

I'm keeping a backup of the latest state of this repo on my machine.

In the same vain, I won't use the ~"C:Verification Extension" label anymore and you can delete it.