Description: Fix building with gtk-doc 1.32

Author: Thomas Andrejak <thomas.andrejak@gmail.com>

Last-Update: 2019-09-13

--- a/docs/api/libpreludedb-docs.xml	2019-09-17 18:49:45.721227852 -0400

+++ b/docs/api/libpreludedb-docs.xml2	2019-09-30 04:06:36.973341933 -0400

@@ -26,10 +26,6 @@

     <xi:include href="xml/preludedb-sql-settings.xml"/>

   </chapter>

-  <chapter id="object-tree">

-    <title>Object Hierarchy</title>

-     <xi:include href="xml/tree_index.sgml"/>

-  </chapter>

   <index id="api-index-full">

     <title>API Index</title>

     <xi:include href="xml/api-index-full.xml"><xi:fallback /></xi:include>