Rm deprecated grandfather 'cel-gaulish' from tests

test/intl402/Locale/extensions-grandfathered.js

@@ -22,18 +22,6 @@ features: [Intl.Locale]
 ---*/
 
 const testData = [
-    // Regular grandfathered without modern replacement.
-    {
-        tag: "cel-gaulish",
-        options: {
-            language: "fr",
-            script: "Cyrl",
-            region: "FR",
-            numberingSystem: "latn",
-        },
-        canonical: "fr-Cyrl-FR-u-nu-latn",
-    },
-
     // Regular grandfathered with modern replacement.
     {
         tag: "art-lojban",