### 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
''' encrypt the supplied file using the provided vault secret '''
        if not context.CLIARGS['args'] and sys.stdin.isatty():
            display.display("Reading plaintext input from stdin", stderr=True)
        for f in context.CLIARGS['args'] or ['-']:
            
            self.editor.encrypt_file(f, self.encrypt_secret,
                                     vault_id=self.encrypt_vault_id,
                                     output_file=context.CLIARGS['output_file'])
        if sys.stdout.isatty():
            display.display("Encryption successful", stderr=True)
    @staticmethod
    def format_ciphertext_yaml(b_ciphertext, indent=None, name=None):
        indent = indent or 10
        block_format_var_name = ""
        if name:
            block_format_var_name = "%s: " % name
        block_format_header = "%s!vault |" % block_format_var_name
        lines = []
        vault_ciphertext = to_text(b_ciphertext)
        lines.append(block_format_header)
        for line in vault_ciphertext.splitlines():
            lines.append('%s%s' % (' ' * indent, line))
        yaml_ciphertext = '\n'.join(lines)
        return yaml_ciphertext
    def execute_encrypt_string(self):