Bug 1564690 [wpt PR 17594] - Update interfaces/css-conditional.idl, a=testonly

Automatic update from web-platform-tests
Update interfaces/css-conditional.idl (#17594)

Source: https://github.com/tidoust/reffy-reports/blob/4daf423/whatwg/idl/css-conditional.idl
Build: https://travis-ci.org/tidoust/reffy-reports/builds/553126765
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wpt-commits: 4beda31498f85ded322ea4d55870973000364ac4
wpt-pr: 17594

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

@@ -7,13 +7,6 @@ partial interface CSSRule {
     const unsigned short SUPPORTS_RULE = 12;
 };
 
-[Exposed=Window]
-interface CSSGroupingRule : CSSRule {
-    readonly attribute CSSRuleList cssRules;
-    unsigned long insertRule (CSSOMString rule, unsigned long index);
-    void deleteRule (unsigned long index);
-};
-
 [Exposed=Window]
 interface CSSConditionRule : CSSGroupingRule {
     attribute CSSOMString conditionText;