[css-color-4] fixed by w3c#3873

Author: svgeesus

css-color-4/Overview.bs

@@ -462,8 +462,6 @@ Resolving <<color>> Values</h3>
 		Each <<system-color>> keyword computes to itself.
 		Its used value is the corresponding color in its color space.
 
-		Issue(3873): Define something for <<deprecated-system-color>>?
-
 	: ''currentcolor''
 	::
 		The ''currentcolor'' keyword computes to itself.