Remove web-style-guide from the site

[deadlight]

Done

Removed the old web style guide section and a reference to it from the /web page

QA

• See that /web-style-guide no longer exists
• See that the section about the web style guide has been removed from /web

Issue / Card

Fixes #66

[webteam-app]

Starting demo at: http://design.ubuntu.com-pr-71.run.demo.haus/