test: remove Windows skipping of http keepalive request GC test

Remove code to skip Windows in test-http-server-keepalive-req-gc. The
test now works reliably on Windows (I think).

PR-URL: https://github.com/nodejs/node/pull/29354


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Сковорода Никита Андреевич <chalkerx@gmail.com>
Reviewed-By: David Carlier <devnexen@gmail.com>