Duplicate types from TypeScript input

```typescript
type AuthTokens = {
accessToken: string;
refreshToken: string;
idToken: string;
};

class UserInfo {
username: string;
password?: string;
tokens?: AuthTokens;
}
```

gives two types for `AuthToken`:

```typescript
export interface AuthTokens {
accessToken: string;
idToken: string;
refreshToken: string;
}

export interface UserInfo {
password?: string;
tokens?: Tokens;
username: string;
}

export interface Tokens {
accessToken: string;
idToken: string;
refreshToken: string;
}
```

This doesn't happen if `AuthTokens` is a `class`, too. The problem is in the JSON Schema that's generated from `typescript-json-schema`.