removed spurious headings

--- a/src/Doc/Datatypes/Datatypes.thy	Tue Jul 30 19:49:42 2013 +0200
+++ b/src/Doc/Datatypes/Datatypes.thy	Tue Jul 30 19:59:17 2013 +0200
@@ -106,14 +106,6 @@
   * Nitpick
 *}
 
-section {* Registering Bounded Natural Functors *}
-
-subsection {* Introductory Example *}
-
-subsection {* General Syntax *}
-
-section {* Generating Free Constructor Theorems *}
-
 section {* Defining Datatypes *}
 
 subsection {* Introductory Examples *}