[Feature Request] Make <a/> tag in headers optional when outputFormat: markdown

**Describe the bug**

A rendered markdown file includes an empty `` tag in the markdown H1 title.
For example:

```
# Delegate CustomBinding0
```

Is this rendered for a reason, or is it a bug? What is the role of this element?

**To Reproduce**
Steps to reproduce the behavior:

Run docfx with `metadata.outputFormat: "markdown"` option.

Whole docfx.json

```json
{
"metadata": [
{
"src": [
{
"src": "..",
"files": [
"**/*.cs"
]
}
],
"dest": "api",
"globalNamespaceId": "Global",
"allowCompilationErrors": true,
"namespaceLayout": "nested",
"outputFormat": "markdown"
}
]
}

```

**Expected behavior**

If rendering this empty `` element is unnecessary, I expect this not to be included in the markdown file.

I'm working on a Unity package project, and I referenced the docfx settings of https://github.com/CaseyHofland/docfx-unitypackage.