Fix duplicated grays

[rauhul]

Removes figure-gray-secondary-alt in favor of figure-gray-tertiary which already had the exact same color values.

Fixes fill-quaternary to have different colors in dark and light mode.

[rauhul]

@swift-ci test

[rauhul]

Note: there is no observable affect of this change on the website visually

[rauhul]

What's the policy on merging this PR, since moving to the swiftlang org I do not seem to be able to merge it myself.

[federicobucchi]

I am waiting for another approval from someone from the working group: https://www.swift.org/website-workgroup/

[rauhul]

Gotcha, is that the general policy? if so would it make sense to require PRs to have 2 approvals?

[federicobucchi]

It is hard to enforce pragmatically specific rules because there are specific people depending on the page and the type of change. Sometimes we need approval from someone in PR (which is included also in the WG). Sometimes 1 approval is enough because the change was discussed / approved in forums.swift.org. So difficult to set a specific unique rule.

[alexandersandberg]

Personally, I think it's better to wait with these smaller improvements/refactors (unless they provide value enough that we don't want to wait with it) until we get a chance to revisit the whole color palette—something we (the website workgroup) want to look into soon.

[kaishin]

@swift-ci test

[rauhul]

@kaishin could we merge this one too?