doc: fix duplicate "this" and "the" on http2.md

PR-URL: https://github.com/nodejs/node/pull/24611


Reviewed-By: Ron Korving <ron@ronkorving.nl>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Denys Otrishko <shishugi@gmail.com>