### 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
edit_parser.add_argument('args', help='Filename', metavar='file_name', nargs='*')
        view_parser = subparsers.add_parser('view', help='View vault encrypted file', parents=[common])
        view_parser.set_defaults(func=self.execute_view)
        view_parser.add_argument('args', help='Filename', metavar='file_name', nargs='*')
        encrypt_parser = subparsers.add_parser('encrypt', help='Encrypt YAML file', parents=[common, output, vault_id])
        encrypt_parser.set_defaults(func=self.execute_encrypt)
        encrypt_parser.add_argument('args', help='Filename', metavar='file_name', nargs='*')
        enc_str_parser = subparsers.add_parser('encrypt_string', help='Encrypt a string', parents=[common, output, vault_id])
        enc_str_parser.set_defaults(func=self.execute_encrypt_string)
        enc_str_parser.add_argument('args', help='String to encrypt', metavar='string_to_encrypt', nargs='*')
        enc_str_parser.add_argument('-p', '--prompt', dest='encrypt_string_prompt',
                                    action='store_true',
                                    help="Prompt for the string to encrypt")
        enc_str_parser.add_argument('--show-input', dest='show_string_input', default=False, action='store_true',
                                    help='Do not hide input when prompted for the string to encrypt')
        enc_str_parser.add_argument('-n', '--name', dest='encrypt_string_names',
                                    action='append',
                                    help="Specify the variable name")
        enc_str_parser.add_argument('--stdin-name', dest='encrypt_string_stdin_name',
                                    default=None,
                                    help="Specify the variable name for stdin")
        rekey_parser = subparsers.add_parser('rekey', help='Re-key a vault encrypted file', parents=[common, vault_id])
        rekey_parser.set_defaults(func=self.execute_rekey)
        rekey_new_group = rekey_parser.add_mutually_exclusive_group()
        rekey_new_group.add_argument('--new-vault-password-file', default=None, dest='new_vault_password_file',
                                     help="new vault password file for rekey", type=opt_help.unfrack_path())
        rekey_new_group.add_argument('--new-vault-id', default=None, dest='new_vault_id', type=str,
                                     help='the new vault identity to use for rekey')
        rekey_parser.add_argument('args', help='Filename', metavar='file_name', nargs='*')
    def post_process_args(self, options):