tls: drop NPN (next protocol negotiation) support

NPN has been superseded by ALPN.  Chrome and Firefox removed support for
NPN in 2016 and 2017 respectively to no ill effect.

Fixes: https://github.com/nodejs/node/issues/14602
PR-URL: https://github.com/nodejs/node/pull/19403


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>