admin/auth/updateUser for MFA not working

Hello. Discovered the following issue using firebase admin v10. I can successfully enroll a user for the MFA process by calling admin.auth().updateUser(...) with multiFactor/enrolledFactors provided. But removing enrolled factors is not successful (https://firebase.google.com/docs/auth/admin/manage-mfa-users):

```
admin.auth().updateUser({
uid: '123456789',
multiFactor: {
enrolledFactors: null,
},
})
.then((userRecord) => {
console.log(userRecord.multiFactor);
})
.catch((error) => {
console.log(error);
});
```
The factors remain in DB. I can see the same discussed for Golang as well here https://github.com/firebase/firebase-admin-go/pull/530/files.