Update all instances of greys in static to use either semantic
colour variables from the toolkit or nearest toolkit grey

• rationalised corresponding grey
• update to semantic variables
• update grey variables to match toolkit rather than static colours
Remove import refernce to local static colours file

• remove reference
• delete _colours.scss

https://www.agileplannerapp.com/boards/105200/cards/5541
Merge pull request #440 from alphagov/remove-refactor-greys-from-static

Remove and refactor local greys from static