[website] Clean up social media links

Summary:
This removes duplicated Twitter link and unwanted Telegram link
Remove "Social Media" section from BCHA page
Add Reddit link to main social media footer info
Telegram link was causing confusion that it was "official", so remove it.

Test Plan: Ran site locally, looked at it and tested links

Reviewers: PiRK, majcosta, josephroyking, #bitcoin_abc

Reviewed By: josephroyking, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D9298