sslutil: move sslkwargs logic into internal function (API)
As the previous commit documented, sslkwargs() doesn't add any
value since its return is treated as a black box and proxied
to wrapsocket().
We formalize its uselessness by moving its logic into a
new, internal function and make sslkwargs() return an empty
dict.
The certificate arguments that sslkwargs specified have been
removed from wrapsocket() because they should no longer be
set.
#require docutils gettext
$ $TESTDIR/check-gendoc it
checking for parse errors