Move archived releases link to release page

Summary:
Now that we have a release page, users will expect to find all releases on there
in one way or another. The archived releases probably do not belong in the nav bar
anyway.

Depends on D7615

Test Plan:
make serve
http://127.0.0.1:4000/releases/

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D7621