[e.cash] Remove upgrade announcement bar

Summary:
It's been a month since the upgrade, so not relevant anymore.
The page at e.cash/upgrade remains available with info about the upgrade.

Test Plan: Run it locally, check that it looks fine.

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D18263