[WEBSITE] Remove relative link conversion in the release notes

Summary: Now that the conversion plugin is working, it's simple to use the proper link type instead of tweaking the release notes.

Test Plan:

./scripts/fetch_documentation.sh

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Subscribers: PiRK

Differential Revision: https://reviews.bitcoinabc.org/D11160