[css-color-4][editorial] remove inadvertent must

Author: svgeesus

css-color-4/Overview.bs

@@ -4961,7 +4961,7 @@ Gamut Mapping
 	Note: this algorithm is for individual, distinct colors;
 	for color images,
 	where relationships between neighboring pixels are important
-	and detail and texture must be preserved,
+	and the aim is to preserve detail and texture,
 	a perceptual rendering intent is more appropriate
 	and in that case,
 	colors inside the destination gamut