lib: remove experimental warning from FormData

fixes: #42792

PR-URL: #42807
Fixes: #42792
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: Mestery <mestery@protonmail.com>
Reviewed-By: Beth Griggs <bgriggs@redhat.com>
Reviewed-By: Filip Skokan <panva.ip@gmail.com>
Reviewed-By: Akhil Marsonya <akhil.marsonya27@gmail.com>

lib/internal/bootstrap/pre_execution.js

@@ -190,12 +190,12 @@ function setupFetch() {
       return undici;
     }
 
-    emitExperimentalWarning('The Fetch API');
     undici = require('internal/deps/undici/undici');
     return undici;
   }
 
   async function fetch(input, init = undefined) {
+    emitExperimentalWarning('The Fetch API');
     return lazyUndici().fetch(input, init);
   }