test_runner: remove outdated comment

Network imports were removed, so remove the comment.

Refs: #53822

lib/test/mock_loader.js

@@ -36,13 +36,6 @@ const { createRequire, isBuiltin } = require('module');
 // https://github.com/nodejs/node/issues/49472
 // or https://github.com/nodejs/node/issues/52219
 
-// TODO(cjihrig): Network imports should be supported. There are two current
-// hurdles:
-// - The module format returned by the load() hook is not known. This could be
-//   implemented as an option, or default to 'module' for network imports.
-// - The generated mock module imports 'node:test', which is not allowed by
-//   checkIfDisallowedImport() in the ESM code.
-
 const mocks = new SafeMap();
 
 async function initialize(data) {