test: remove message from strictEqual assertions

When an AssertionError happens, the value of headers['set-cookie']
is not reported. That information is useful for debugging.
Hence removed the value passed as the message in deepStrictEqual
assertions of test/parallel/test-http2-cookies.js

Backport-PR-URL: https://github.com/nodejs/node/pull/22850
PR-URL: https://github.com/nodejs/node/pull/20174


Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>