Bug 1510638 [wpt PR 14275] - Update interfaces/css-fonts.idl, a=testonly

Automatic update from web-platform-tests
Update interfaces/css-fonts.idl (#14275)

Source: https://github.com/tidoust/reffy-reports/blob/6f59720/whatwg/idl/css-fonts.idl
Build: https://travis-ci.org/tidoust/reffy-reports/builds/460633569
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wpt-commits: fa478aee49d2d9bee362c456f7d70db47cdc921a
wpt-pr: 14275

testing/web-platform/tests/interfaces/css-fonts.idl

@@ -29,7 +29,7 @@ partial interface CSSRule {
 };
 
 interface CSSFontPaletteValuesRule : CSSRule {
-  maplike<unsigned long, (CSSOMString or CSSOMRGBColor)>;
+  maplike<unsigned long, CSSOMString>;
   attribute CSSOMString fontFamily;
   attribute CSSOMString basePalette;
 };