[e.cash] Deprecate legacy landing page

Summary:
Lose web/e.cash_v2 and replace the web/e.cash with the new site. Update CI.

I am not familiar with how this is deployed in CI, may need to update some configs there before landing.

Test Plan: test a build, tho I'm not sure, maybe we expect a failure after changing / removing things here

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D18760