Delete super old migration documentation

Author: PowerKiKi

_data/sidebar.yml

@@ -10,8 +10,6 @@ entries:
       items:
         - title: Get started
           url: /get_started/
-        - title: How to migrate
-          url: /how-to/migrate/
         - title: How to upgrade
           url: /how-to/upgrade/
         - title: How to maintain

pages/documentation/how-to/migrate.md

@@ -8,8 +8,7 @@ layout: homepage
   <div class="col-lg-6">
     <h2>Stable version</h2>
     <p>This is the latest stable version : <span class="label label-success">{{ site.data.project.release.version }}</span></p>
-    <p>Once downloaded, follow the <a href="{{ site.baseurl }}/get_started/">Step by Step installation guide</a> or the
-      <a href="{{ site.baseurl }}/how-to/migrate/">Step by Step migration guide</a>.</p>
+    <p>Once downloaded, follow the <a href="{{ site.baseurl }}/get_started/">Step by Step installation guide</a>.</p>
 
     <ul class="release-downloads">
       <li>

pages/download/index.md

@@ -3,7 +3,6 @@ title: How-To
 permalink: /how-to/
 ---
 
-* [How to migrate]({{ site.base_url }}/how-to/migrate/)
 * [How to upgrade]({{ site.base_url }}/how-to/upgrade/)
 * [How to maintain]({{ site.base_url }}/how-to/maintain/)
 * [How to remove]({{ site.base_url }}/how-to/remove/)