[images-4] Remove double section of image-set()

image-set() was pushed back to Images 4, so a double section was added in af2c881, with one referring to Images 3 and the other containing the true definition. Remove the section referencing Images 3.

Author: csnardi

css-images-4/Overview.bs

@@ -363,22 +363,6 @@ Image Fallbacks and Annotations: the ''image()'' notation {#image-notation}
 	</div>
 
 
-<!--
-████ ██     ██    ███     ██████   ████████          ██████  ████████ ████████   ███ ███
- ██  ███   ███   ██ ██   ██    ██  ██               ██    ██ ██          ██     ██     ██
- ██  ████ ████  ██   ██  ██        ██               ██       ██          ██    ██       ██
- ██  ██ ███ ██ ██     ██ ██   ████ ██████   ███████  ██████  ██████      ██    ██       ██
- ██  ██     ██ █████████ ██    ██  ██                     ██ ██          ██    ██       ██
- ██  ██     ██ ██     ██ ██    ██  ██               ██    ██ ██          ██     ██     ██
-████ ██     ██ ██     ██  ██████   ████████          ██████  ████████    ██      ███ ███
--->
-
-
-Resolution Negotiation: the ''image-set()'' notation {#image-set-notation}
---------------------------------------------------------------------------
-
-Note: No change from [[css3-images]].
-
 <!--
  ██████  ████████   ███████   ██████   ██████          ████████    ███    ████████  ████████   ███ ███
 ██    ██ ██     ██ ██     ██ ██    ██ ██    ██         ██         ██ ██   ██     ██ ██        ██     ██