test: remove outdated V8 flag

The flag is going to be removed upstream in V8 9.0.

Refs: v8/v8@0a480c3

PR-URL: #37151
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Richard Lau <rlau@redhat.com>
Reviewed-By: Jiawen Geng <technicalcute@gmail.com>
Reviewed-By: Darshan Sen <raisinten@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>

test/node-api/test_buffer/test.js

@@ -1,5 +1,5 @@
 'use strict';
-// Flags: --expose-gc --no-concurrent-array-buffer-freeing --no-concurrent-array-buffer-sweeping
+// Flags: --expose-gc --no-concurrent-array-buffer-sweeping
 
 const common = require('../../common');
 const binding = require(`./build/${common.buildType}/test_buffer`);