[bitcoinabc.org] Remove the twitter timeline

Summary: It's no longer working and displays "No tweet yet", so remove it temporarly until the issue is fixed upstream.

Test Plan:

jekyll bundle exec serve

Check the Twitter timeline is no longer displayed on the index page.

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D14281