Remove 'About' link to GDS wiki

The tdt-documentation is for users across government which means there 
is a group of users who won't be able to access the About link. If we 
want to keep the link to the GDS wiki, it should be somewhere less 
proeminent.

config/tech-docs.yml

@@ -9,7 +9,6 @@ phase: Beta
 
 # Links to show on right-hand-side of header
 header_links:
-  About: https://sites.google.com/a/digital.cabinet-office.gov.uk/gds/communities-of-practice/content/technical-writing
   Support: /support
 
 # Table of contents depth – how many levels to include in the table of contents.