Remove misleading claims from contrast documentation

[xi]

I believe the documentation on contrast algorithms contains some misleading claims. See also http://tobib.spline.de/xi/posts/2022-09-10-contrast-algorithms/

[svgeesus]

These proposed https://github.com/xi/apca-introduction/issues/6changes are factually incorrect (Lightness is by definition perceptually uniform while luminance is not, and is not intended to be).

You are free to do what you wish on your own site, including "evaluating" a known-incorrect version of APCA that you have devised, and to ignore and close issues raised against it:

• "All models are wrong....but some models are useful" xi/apca-introduction#8
• Flare correction of 0.4 (40%) xi/apca-introduction#3
• xi claims that he can see no difference regarding examples demonstrating the deficiency of WCAG2 vs the demonstrated efficacy of APCA xi/apca-introduction#6
• Visual Examples are Incorrect and Misleading xi/apca-introduction#18

but please don't try to spread that sort of stuff to this site.

I will explain why I am closing this, with a quote of yours:

I understand that you do not agree with this analysis, but please do not spam this issue tracker. This is not an issue.

[xi]

I am sorry you see it this way. I didn't realize that these changes were controversial. But I don't want to escalate anything so I accept that you rejected this pull request.