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 <[email protected]>
Reviewed-By: Anna Henningsen <[email protected]>
Reviewed-By: Yuta Hiroto <[email protected]>
Reviewed-By: Colin Ihrig <[email protected]>
Reviewed-By: Ruben Bridgewater <[email protected]>
Reviewed-By: Luigi Pinca <[email protected]>
Reviewed-By: James M Snell <[email protected]>