[css-color-4] Remove mention of custom color spaces from intro (moved to color 5)

Author: svgeesus

css-color-4/Overview.bs

@@ -158,12 +158,7 @@ Introduction</h2>
 	previously, the more saturated colors outside the sRGB gamut
 	could not be used in CSS
 	even if the display device supported them.
-	In addition to the family of
-	<abbr title="red-green-blue">RGB</abbr> color spaces,
-	[=color spaces=] with other primaries
-	such as <abbr title="cyan-magenta-yellow-black">CMYK</abbr> or
-	<abbr title="black-cyan-magenta-yellow-green-orange-violet">KCMYGOV</abbr>
-	are supported.
+	
 
 	A <a href="https://test.csswg.org/harness/results/css-color-4_dev/grouped/">draft implementation report</a> is available.