### Summary

Running `ansible-doc -l` generates 430 deprecation warnings on stderr before printing anything to stdout.
```
[DEPRECATION WARNING]: amazon.aws.aws_az_facts has been deprecated.
aws_az_facts was renamed in Ansible 2.9 to aws_az_info. Please update your
tasks. This feature will be removed from amazon.aws in a release after
2022-06-01. Deprecation warnings can be disabled by setting
deprecation_warnings=False in ansible.cfg.

[DEPRECATION WARNING]: amazon.aws.aws_caller_facts has been deprecated.
aws_caller_facts was renamed in Ansible 2.9 to aws_caller_info. Please update
your tasks. This feature will be removed from amazon.aws in a release after
2021-12-01. Deprecation warnings can be disabled by setting
deprecation_warnings=False in ansible.cfg.
...
```

### Issue Type

Bug Report

### Component Name

ansible-doc

### Ansible Version

```console
$ ansible-doc --version

ansible-doc 2.10.6
  config file = None
  configured module search path = [u'/home/charleshowes/.ansible/plugins/modules', u'/usr/share/ansible/plugins/modules']
  ansible python module location = /usr/local/lib/python2.7/dist-packages/ansible
  executable location = /usr/local/bin/ansible-doc
  python version = 2.7.17 (default, Sep 30 2020, 13:38:04) [GCC 7.5.0]
```


### Configuration

```console
$ ansible-config dump --only-changed
(no output)
```


### OS / Environment

Ubuntu 18.04

### Steps to Reproduce

<!--- Paste example playbooks or commands between quotes below -->
```shell (paste below)
ansible-doc -l
```


### Expected Results

I expected to see a list of available plugins, and was shocked to have pages and pages of warnings.

### Actual Results

```console
$ ansible-doc -l 2>&1 | head

[DEPRECATION WARNING]: amazon.aws.aws_az_facts has been deprecated. 
aws_az_facts was renamed in Ansible 2.9 to aws_az_info. Please update your 
tasks. This feature will be removed from amazon.aws in a release after 
2022-06-01. Deprecation warnings can be disabled by setting 
deprecation_warnings=False in ansible.cfg.
[DEPRECATION WARNING]: amazon.aws.aws_caller_facts has been deprecated. 
aws_caller_facts was renamed in Ansible 2.9 to aws_caller_info. Please update 
your tasks. This feature will be removed from amazon.aws in a release after 
2021-12-01. Deprecation warnings can be disabled by setting 
deprecation_warnings=False in ansible.cfg.

$ ansible-doc -l 2>&1 | grep -c 'DEPRECATION WARNING'

430
```


### Code of Conduct

- [X] I agree to follow the Ansible Code of Conduct
try:
                full_paths = (os.path.join(b_path, f) for f in os.listdir(b_path))
            except OSError as e:
                display.warning("Error accessing plugin paths: %s" % to_text(e))
            for full_path in (to_native(f) for f in full_paths if os.path.isfile(f) and not f.endswith(b'__init__.py')):
                full_name = os.path.basename(full_path)
                
                
                
                if any(full_path.endswith(x) for x in C.MODULE_IGNORE_EXTS):
                    continue
                splitname = os.path.splitext(full_name)
                base_name = splitname[0]
                try:
                    extension = splitname[1]
                except IndexError:
                    extension = ''
                
                full_path = to_text(full_path, errors='surrogate_or_strict')
                
                if base_name not in self._plugin_path_cache['']:
                    self._plugin_path_cache[''][base_name] = PluginPathContext(full_path, internal)
                if full_name not in self._plugin_path_cache['']:
                    self._plugin_path_cache[''][full_name] = PluginPathContext(full_path, internal)
                if base_name not in self._plugin_path_cache[extension]:
                    self._plugin_path_cache[extension][base_name] = PluginPathContext(full_path, internal)
                if full_name not in self._plugin_path_cache[extension]:
                    self._plugin_path_cache[extension][full_name] = PluginPathContext(full_path, internal)
            self._searched_paths.add(path)
            try: