Revert fetching asset_io on wasm

kayak_font/src/ttf/loader.rs

@@ -32,6 +32,7 @@ impl AssetLoader for TTFLoader {
         load_context: &'a mut LoadContext,
     ) -> BoxedFuture<'a, Result<(), anyhow::Error>> {
         Box::pin(async move {
+            #[cfg(not(target_family = "wasm"))]
             let asset_io = load_context
                 .asset_io()
                 .downcast_ref::<FileAssetIo>();