This shared secret was used when cubicweb web server was living outside of the
data repository and forward requests with pyro.
We do not support pyro anymore so this is useless.

Just drop all related crypto code and drop the option
'trustedauth-secret-key-file' and drop the dependency on cryptodome/pycrypto.

Use a special kwargs "trustedauth_login", our BaseAuthentifier only match with
our WebAuthInfoRetriever.

As a side effect, this fix test/unittest_trustedauth.py which were broken in python 3 :)