bug#33047: pypi importer uses incorrect package names

[Julien Lepiller]

Hi,

I found that sometimes the pypi importer had trouble importing packages 
correctly. For instance, running "guix import pypi txaio" gave me this 
list of dependencies:

(propagated-inputs
 `(("python-[all]" ,#{python-\x5b;all\x5d;}#)
   ("python-[asyncio]"
    ,#{python-\x5b;asyncio\x5d;}#)
   ...))

guix import pypi magic-wormhole had this:

(propagated-inputs
  ("python-autobahn[twisted]"
   ,#{python-autobahn\x5b;twisted\x5d;}#)
  ...))

Of course, they break the recursive importer, which makes it difficult 
to import these packages correctly.