Fix MuJoCo WASM loader imports

wasm/demo_app/app.ts

@@ -16,8 +16,6 @@ import * as THREE from "three"
 import { OrbitControls } from "three/examples/jsm/controls/OrbitControls.js"
 import loadMujoco from "../dist/mujoco.js"
 
-declare function loadMujoco(): Promise<MainModule>;
-
 let mujoco: any;
 
 const modelXml = `
@@ -483,7 +481,7 @@ async function main() {
 
   } catch (error) {
     console.error('Initialization error: ', error);
-    app.dispose();
+    app?.dispose();
   }
 }
 main();

wasm/tests/sandbox/main.ts

@@ -15,8 +15,6 @@
 import { MainModule, MjData, MjModel } from "../../dist/mujoco"
 import loadMujoco from "../../dist/mujoco.js"
 
-declare function loadMujoco(): Promise<MainModule>;
-
 async function main() {
   const mujoco: MainModule = await loadMujoco();