configure: make the TLS library choice(s) explicit

configure: make the TLS library choice(s) explicit

configure no longer tries to find a TLS library by default, but all
libraries are now equal: the user needs to explicitly ask what TLS
library or libraries to use.

If no TLS library is selected, configure will error out unless
--without-ssl is explicitly used to request a built without TLS (as that
is very rare these days).

Removes: --with-winssl, --with-darwinssl and all --without-* options for
TLS libraries.

Closes #6897