test: use expectsError in test-debug-agent.js

Use common.expectsError() in place of inline validation function in
test-debug-agent.js.

PR-URL: https://github.com/nodejs/node/pull/11410
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>

test/parallel/test-debug-agent.js

@@ -1,12 +1,13 @@
 'use strict';
-require('../common');
+const common = require('../common');
 const assert = require('assert');
 const debug = require('_debug_agent');
 
 assert.throws(
   () => { debug.start(); },
-  function(err) {
-    return (err instanceof assert.AssertionError &&
-            err.message === 'Debugger agent running without bindings!');
-  }
+  common.expectsError(
+    undefined,
+    assert.AssertionError,
+    'Debugger agent running without bindings!'
+  )
 );