Consolidate remaining colors into variables (#21582)

Consolidate remaining colors into variables (#21582)

Remove remaining non-color variables in arc-green, so the theme is now
100% defined from variables (excluding inverts). Adjusted red/green to
match previous overwritten colors.

`--color-gold-light` is removed, it was unused and is not part of
fomantic colors.

<img width="772" alt="Screen Shot 2022-10-24 at 20 22 25"
src="https://user-images.githubusercontent.com/115237/197599339-1d1bf6e3-aa90-4f38-9753-24effd4b178d.png">
<img width="275" alt="Screen Shot 2022-10-24 at 20 25 52"
src="https://user-images.githubusercontent.com/115237/197599344-79c1d3ac-c709-4e30-a60b-4738af672c12.png">
<img width="446" alt="Screen Shot 2022-10-24 at 20 26 46"
src="https://user-images.githubusercontent.com/115237/197599346-f2ef6449-7efd-4f81-bbb6-e7bee4528f50.png">

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>