Remove twitter, add other socials

Remove twitter in the one page (https://github.com/carpentries/commons/blob/carpentries-is-singular/about-carpentries/carpentries-one-pager.md) and replace with other socials.

Open about-carpentries/carpentries-one-pager.md and inspect the current Twitter entry and surrounding social links. Remove Twitter and add the other social links intended by the issue; the work is done when the one-pager no longer lists Twitter and includes the replacements.

Written by the indexing model from the issue text.