src: remove process._debugPause()

This method is undocumented and depends on a V8 API that is slated for
removal.  The inspector and node-inspect don't use it and I could find
no third-party code that depends on it.  Remove it.

PR-URL: https://github.com/nodejs/node/pull/17060


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Evan Lucas <evanlucas@me.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Timothy Gu <timothygu99@gmail.com>