### Summary

`ansible-vault encrypt_string --help` shows the `--output` option but it remains without effect.

### Issue Type

Bug Report

### Component Name

ansible-vault

### Ansible Version

```console
$ ansible --version
ansible 2.9.21
  config file = /etc/ansible/ansible.cfg
  configured module search path = ['/home/elavarde/.ansible/plugins/modules', '/usr/share/ansible/plugins/modules']
  ansible python module location = /usr/lib/python3.9/site-packages/ansible
  executable location = /usr/bin/ansible
  python version = 3.9.5 (default, May 14 2021, 00:00:00) [GCC 11.1.1 20210428 (Red Hat 11.1.1-1)]
```


### Configuration

```console
$ ansible-config dump --only-changed
[... empty ...]
```


### OS / Environment

Fedora 34

### Steps to Reproduce

```shell
ansible-vault encrypt_string --ask-vault-pass --name myvar --output vault.yml 'some secret'
```


### Expected Results

Variable and its encrypted content are written to file and not to stdout _or_ the option `--output` isn't shown in the help.

Making the `--output` version working would probably be a duplicate of issue #59590, so probably removing the `--output` option which doesn't work could be a simpler step. More important for now is that it's consistent.

### Actual Results

```console
- output file isn't created/edited
- variable and its content are output to stdout
```


### Code of Conduct

- [X] I agree to follow the Ansible Code of Conduct
stderr=True)
                display.display('The last named variable will be "%s". The rest will not have'
                                ' names.' % context.CLIARGS['encrypt_string_names'][-1],
                                stderr=True)
            
            for extra_arg in args[len(name_and_text_list):]:
                name_and_text_list.append((None, extra_arg))
        
        else:
            name_and_text_list = [(None, x) for x in args]
        
        for name_and_text in name_and_text_list:
            name, plaintext = name_and_text
            if plaintext == '':
                raise AnsibleOptionsError('The plaintext provided from the command line args was empty, not encrypting')
            b_plaintext = to_bytes(plaintext)
            b_plaintext_list.append((b_plaintext, self.FROM_ARGS, name))
        
        
        outputs = self._format_output_vault_strings(b_plaintext_list, vault_id=self.encrypt_vault_id)
        for output in outputs:
            err = output.get('err', None)
            out = output.get('out', '')
            if err:
                sys.stderr.write(err)
            print(out)
        if sys.stdout.isatty():
            display.display("Encryption successful", stderr=True)
        
    def _format_output_vault_strings(self, b_plaintext_list, vault_id=None):