Switch from title frontmatter to H1 in migration tool

[bmorelli25]

We initially asked for the adoc-to-md tool to convert page titles to frontmatter. We no longer want to do that.

Instead of

---
title: "What is Elasticsearch?"
---

// content

The migration tool should output:

# What is Elasticsearch?

// content

If there is a titleabrev:

== EQL pipe reference
++++
<titleabbrev>Pipe reference</titleabbrev>
++++

The output should be

---
navigation_title: "Pipe reference"
---

# EQL pipe reference

// content

[bmorelli25]

Fixed in migration tooling.