Merge branch '474646-remove-btn-class-from-button-scss-part-2' into 'master'

Remove "btn" class from buttons.scss

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/167831



Merged-by: Imre Farkas <ifarkas@gitlab.com>
Approved-by: Thomas Hutterer <thutterer@gitlab.com>
Approved-by: Hunter Stewart <hustewart@gitlab.com>
Approved-by: Scott de Jonge <sdejonge@gitlab.com>
Approved-by: Imre Farkas <ifarkas@gitlab.com>
Reviewed-by: Mark Florian <mflorian@gitlab.com>
Reviewed-by: Scott de Jonge <sdejonge@gitlab.com>
Co-authored-by: James Rushford <jrushford@gitlab.com>