[e.cash] Change Twitter logo to X

Summary:
Use their new corporate branding.
Source: https://about.twitter.com/en/who-we-are/brand-toolkit
Left the link as twitter.com, since x.com seems to redirect there anyway

Part of T3297

Test Plan: Ran it locally, looks fine and link works

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D14684