refactor: simplify code

Author: Loïc Mangeonjean

src/MonacoEditor.tsx

@@ -215,12 +215,11 @@ function MonacoEditor ({
       if (fileUri != null) {
         const uri = monaco.Uri.parse(fileUri)
 
-        const fileDisposable = registerFile(new RegisteredMemoryFile(uri, value!))
+        disposableStore.add(registerFile(new RegisteredMemoryFile(uri, value!)))
 
         const modelIRefPromise = createModelReference(uri)
         disposableStore.add({
           dispose () {
-            fileDisposable.dispose()
             void modelIRefPromise.then(modelIRef => modelIRef.dispose(), console.error)
           }
         })