revert branded type change

packages/svelte/src/attachments/public.d.ts

@@ -1,9 +1,4 @@
-declare const brand: unique symbol;
-type Brand<B> = { [brand]: B };
-type Branded<T, B> = T & Brand<B>;
-type AttachmentsKeySymbol = Branded<symbol, 'svelte.attachments'>;
-
 /**
  * A unique symbol used for defining the attachments to be applied to an element or component.
  */
-export const AttachmentsKey: AttachmentsKeySymbol;
+export const AttachmentsKey: unique symbol;