Remove crufty config variables (jupyter#645)

Author: palewire

_config.yml

@@ -7,8 +7,6 @@ description: > # this means to ignore newlines until "baseurl:"
     interactive dashboards and other media.
 baseurl: "" # the subpath of your site, e.g. /blog/
 url: "https://jupyter.org" # the base hostname & protocol for your site
-twitter_username: ProjectJupyter
-github_username:  Jupyter
 
 # Build settings
 markdown: kramdown