fix debug log message when userid is None

[eyetheekh]

summary

The log message formats the string using % userid, but the string does not contain a formatting placeholder, which causes:

TypeError: not all arguments converted during string formatting

This removes the % userid from the log message since its None anyway.

to reproduce

from pyramid.authentication import RepozeWho1AuthenticationPolicy

class DummyRequest:
    environ = {"repoze.who.identity": {"repoze.who.userid": None}}

def _log(msg, methodname, request):
    print(msg)

policy = RepozeWho1AuthenticationPolicy()
policy.debug = True
policy._log = _log

request = DummyRequest()
result = policy.authenticated_userid(request)  # raises type error