Make "rlogin" method obsolete in url*.el

Make "rlogin" method obsolete in url*.el

* lisp/url/url-about.el (url-probe-protocols): Remove "rlogin".
* lisp/url/url-gw.el (url-gateway-rlogin-host)
(url-gateway-rlogin-user-name, url-gateway-rlogin-parameters)
(url-open-rlogin): Make obsolete.  (Bug#56891)
(url-open-stream):
* lisp/url/url-misc.el (url-do-terminal-emulator): Warn when using
"rlogin".
(url-rlogin): Make obsolete.
* lisp/url/url-vars.el (url-gateway-method): Remove "rlogin"
choice.

* lisp/url/url-gw.el (url-gw-rlogin-obsolete-warned-once)
* lisp/url/url-misc.el (url-misc-rlogin-obsolete-warned-once): New
variables, immediately marked obsolete.

* doc/misc/url.texi (telnet/tn3270): Rename section from
"rlogin/telnet/tn3270".
(Gateways in general, Customization): Don't mention "rlogin"
method.