Emacs: Use built-in url.el instead of request.el

[sfllaw]

The tclip Emacs package depends on request.el, which is a third-party package:

tclip/contrib/tclip.el

Lines 14 to 15 in 75434de

	;; This uses request-el to make requests to your tailnet's tclip server. You
	;; can install request-el with M-x package-install.

We can remove this dependency by relying on the built-in URL package.