debugger: remove unused code

Remove code that was for when `node-inspect` was called as a standalone
process.

PR-URL: nodejs#38161
Backport-PR-URL: nodejs#38858
Refs: nodejs#36481
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Jan Krems <jan.krems@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Stephen Belanger <admin@stephenbelanger.com>
Reviewed-By: Gerhard Stöbich <deb2001-github@yahoo.de>
Reviewed-By: Michaël Zasso <targos@protonmail.com>

lib/internal/inspector/_inspect.js

@@ -29,16 +29,7 @@ const { EventEmitter } = require('events');
 const net = require('net');
 const util = require('util');
 
-const runAsStandalone = typeof __dirname !== 'undefined';
-
 const { 0: InspectClient, 1: createRepl } =
-  runAsStandalone ?
-  // This copy of node-inspect is on-disk, relative paths make sense.
-    [
-      require('./inspect_client'),
-      require('./inspect_repl'),
-    ] :
-  // This copy of node-inspect is built into the node executable.
     [
       require('internal/inspector/inspect_client'),
       require('internal/inspector/inspect_repl'),
@@ -336,9 +327,7 @@ function startInspect(argv = process.argv.slice(2),
                       stdin = process.stdin,
                       stdout = process.stdout) {
   if (argv.length < 1) {
-    const invokedAs = runAsStandalone ?
-      'node-inspect' :
-      `${process.argv0} ${process.argv[1]}`;
+    const invokedAs = `${process.argv0} ${process.argv[1]}`;
 
     console.error(`Usage: ${invokedAs} script.js`);
     console.error(`       ${invokedAs} <host>:<port>`);