### 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
if hide_input:
                msg = "String to encrypt (hidden): "
            else:
                msg = "String to encrypt:"
            prompt_response = display.prompt(msg, private=hide_input)
            if prompt_response == '':
                raise AnsibleOptionsError('The plaintext provided from the prompt was empty, not encrypting')
            b_plaintext = to_bytes(prompt_response)
            b_plaintext_list.append((b_plaintext, self.FROM_PROMPT, name))
        
        if self.encrypt_string_read_stdin:
            if sys.stdout.isatty():
                display.display("Reading plaintext input from stdin. (ctrl-d to end input, twice if your content does not already have a newline)", stderr=True)
            stdin_text = sys.stdin.read()
            if stdin_text == '':
                raise AnsibleOptionsError('stdin was empty, not encrypting')
            if sys.stdout.isatty() and not stdin_text.endswith("\n"):
                display.display("\n")
            b_plaintext = to_bytes(stdin_text)
            
            name = context.CLIARGS['encrypt_string_stdin_name']
            b_plaintext_list.append((b_plaintext, self.FROM_STDIN, name))
        
        
        if context.CLIARGS.get('encrypt_string_names', False):
            name_and_text_list = list(zip(context.CLIARGS['encrypt_string_names'], args))
            
            if len(args) > len(name_and_text_list):
                
                display.display('The number of --name options do not match the number of args.',