Remove outdated statement related to HCT and achromatic values

We no longer try and calculate the achromatic curve based on RGB.
The achromatic values are now calculated relative to the color space,
and if a color space has complex achromatic curves due to background and
adapting luminance considerations we accept those values.

coloraide/spaces/hct.py

@@ -5,11 +5,6 @@
 We simply, as described, create a color space with CIELAB L* and CAM16's C and h components.
 Environment settings are calculated with the assumption of L* 50.
 
-As ColorAide usually cares about setting powerless hues as NaN, especially for good interpolation,
-we've also calculated the cut off for chromatic colors and will properly enforce achromatic, powerless
-hues. This is because CAM16 actually resolves colors as achromatic before chroma reaches zero as
-lightness increases. In the SDR range, a Tone of 100 will have a cut off as high as ~2.87 chroma.
-
 Generally, the HCT color space is restricted to sRGB and SDR range in the Material library, but we do
 not have such restrictions.