[css-color-5] remove incorrect image

Author: Chris Lilley

css-color-5/Overview.bs

@@ -163,8 +163,9 @@ Mixing colors: the ''color-mix'' function {#colormix}
 	This example demonstrates that not all colors which can be mixed, can be displayed on current devices.
 </div>
 
+<!--
 <img src="images/mix_red_yellow_lightness30.png" alt="Result of mix-color(red, yellow, lightness(30%)" />
-<!-- this image incorrectly shows red and yellow to be outside gamut as well, which is confusing.
+ this image incorrectly shows red and yellow to be outside gamut as well, which is confusing.
      it also shows the result color after per-component clipping, which is not desirable -->
 
 Instead of a list of color functions,