[css-color-4] remove gray function as name sucks

Author: svgeesus

css-color-4/Overview.bs

@@ -187,7 +187,7 @@ Representing Colors: the <<color>> type</h2>
 	<pre class='prod'>
 	&lt;color> = <<hex-color>> | <<named-color>> | currentcolor | transparent
 	          <<rgb()>> | <<rgba()>> | <<hsl()>> | <<hsla()>> | <<hwb()>> |
-	          <<lab()>> | <<lch()>> | <<gray()>> |
+	          <<lab()>> | <<lch()>> |
 	          <<color()>> | <<device-cmyk()>> |
 	          <<system-color>>
 	</pre>
@@ -247,7 +247,7 @@ Resolving <<color>> Values</h3>
 		paired with the specified alpha channel
 		(defaulting to opaque if unspecified).
 
-	: ''lab()'', ''lch()'', and ''gray()'' values
+	: ''lab()'' and ''lch()'' values
 	::
 		The computed and used value
 		is the corresponding CIE Lab color
@@ -1932,41 +1932,9 @@ Converting LCH colors to Lab  colors</h3>
 		<li>L is the same
 	</ol>
 
-<h2 id='grays'>
-Specifying Grays: the ''gray()'' functional notation</h2>
-
-	Issue(290):
-
-	Grays are fully desaturated colors.
-	The ''gray()'' functional notation simplifies specifying this common set of colors,
-	so that only a single numerical parameter is required,
-	and so that gray(50%) is a visual mid-gray
-	(perceptually equidistant between black and white).
-
-	<pre class='prod'>
-	<dfn>gray()</dfn> = gray( <<percentage>>  [ / <<alpha-value>> ]? )
-	</pre>
-
-	The first argument specifies the shade of gray,
-	equal to the CIE Lightness,
-	while the second optional argument specifies the alpha channel of the gray.
-
-	Note: In other words,
-	''gray(a% / b)'' is equal to ''lab(a% 0 0 / b)''.
-
-<h3 id='gray-to-rgb'>
-Converting gray colors to sRGB  colors</h3>
-
-	Conversion from gray to sRGB requires multiple steps;
-	in practice all but the last step are linear calculations and can be combined.
-
-	<ol>
-		<li>Convert to Lab by setting L to the gray value, a and b to 0
-		<li>Convert Lab to XYZ
-		<li>Adapt from D50 to D65 (Bradford transform)
-		<li>Convert from (D65-adapted) CIE XYZ to linear sRGB
-		<li>Convert from linear-light sRGB to sRGB (do gamma encoding)
-	</ol>
+<!-- gray() removed in #4621
+https://github.com/w3c/csswg-drafts/issues/4621
+-->
 
 <h2 id='icc-colors'>
 Profiled, Device-dependent Colors</h2>
@@ -2791,7 +2759,6 @@ Changes from Colors 3</h3>
 	Several brand new features have been added:
 
 	<ol>
-		<li>''gray()'' function, for specifying grays compactly.
 
 		<li>''hwb()'' function, for specifying colors in the HWB notation.