[css-color-4] Remove check on missing values for HTML-compatible serialization, they will already have been converted to zero w3c#10550

Author: svgeesus

css-color-4/Overview.bs

@@ -6207,7 +6207,6 @@ Serializing sRGB values</h3>
 	<ol>
 		<li>The color space is sRGB</li>
 		<li>The alpha is 1</li>
-		<li>There are no [=missing=] values</li>
 		<li>The RGB component values are internally represented as integers between 0 and 255 inclusive (i.e. 8-bit unsigned integer)</li>
 		<li><dfn export for="color serialization">HTML-compatible serialization is requested</dfn></li>
 	</ol>