remove relative gray following #4621

Author: svgeesus

css-color-5/Overview.bs

@@ -329,19 +329,3 @@ When an origin color is present, the following keywords can also be used in this
 	The result is <span class="swatch" style="--color: rgb(57.58%, 32.47%, 3.82%)"> </span> lch(49.80256% 54.0114 63.6769)
 </div>
 
-<h4>Relative grayscale colors</h4>
-
-The grammar of the ''gray()'' function is extended as follows:
-
-<pre class='prod'>
-<dfn>gray()</dfn> = gray([from <<color>>]? <<number>>  [ / <<alpha-value>> ]? )
-</pre>
-
-When an origin color is present, the following keywords can also be used in this function (provided the end result conforms to the expected type for the parameter) and correspond to:
-
-- 'l' is a <<percentage>> that corresponds to the origin color's CIE Lightness
-- 'alpha' is a <<percentage>> that corresponds to the origin color's alpha transparency
-
-<div class="example">
-	''gray(from var(--base-color) l)'' produces a grayscale version of ''var(--base-color)'' with the same lightness.
-</div>