[e.cash] Remove QUIC from roadmap

Summary:
Work on this is stalled, and it's unclear if it will be resumed,
or some other networking improvements will be added instead.

Test Plan: Ran the site locally, looks good.

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D15173