Apply suggestions from code review

Author: Rich-Harris

packages/create-svelte/templates/default/src/app.d.ts

@@ -10,6 +10,4 @@ declare global {
 	}
 }
 
-// This line ensures this file is treated as a module.
-// It can be removed if you add an import to this file.
-export default undefined;
+export {};

packages/create-svelte/templates/skeleton/src/app.d.ts

@@ -10,6 +10,4 @@ declare global {
 	}
 }
 
-// This line ensures this file is treated as a module.
-// It can be removed if you add an import to this file.
-export default undefined;
+export {};

packages/create-svelte/templates/skeletonlib/src/app.d.ts

@@ -10,6 +10,4 @@ declare global {
 	}
 }
 
-// This line ensures this file is treated as a module.
-// It can be removed if you add an import to this file.
-export default undefined;
+export {};