Remove remaining grey buttons

A few months ago we reviewed our button styling and decided to remove grey buttons altogether. From https://gitlab.com/gitlab-org/gitlab-ce/issues/25220:

Proposal

  • Keep the outline buttons white filled

A few grey buttons still remain, specifically in the Project, Group and User Profile pages:

Project page Group page User page
Screenshot_2018-03-15_18.03.50 Screenshot_2018-03-15_18.06.50 Screenshot_2018-03-15_18.06.58

Proposal

Update these remaining buttons to the current style with a white background and remove the deprecated buttons from the codebase.