test: remove obsolete debugger tests

The tests in `test/debugger` all fail since the removal of the
pre-inspector debugger (if they weren't already failing). They do not
run in CI (probably because they were never reliable). Remove them and
associated fixtures.

PR-URL: nodejs/node#15139
Reviewed-By: Eugene Ostroukhov <eostroukhov@google.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Yuta Hiroto <hello@about-hiroppy.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>