async_hooks: remove deprecated APIs

These APIs were introduced during the lifetime of Node 8 in an
experimental API and should safely be removable in Node 9+.

PR-URL: https://github.com/nodejs/node/pull/14414


Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Andreas Madsen <amwebdk@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Rich Trott <rtrott@gmail.com>