removing reference to column-gap-image

Author: howcom

css3-multicol/Overview.src.html

@@ -1592,10 +1592,6 @@ <h2>Conformance</h2>
 <p>Conforming UAs must flow the content of an element into several
 columns according to this specification.
 
-<p>User agents that support CSS3 Backgrounds and Borders
-[[!CSS3BG]] must support 'column-gap-image'; for other
-UAs this property is optional.
-
 <p>The conformance requirements are expressed with a combination of
     descriptive assertions and RFC 2119 terminology. The key words "MUST",
     "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT",