Mach's GFDL documentation is not DFSG-free, we need to drop the build rules.

Index: b/Makefile.am
===================================================================
--- a/Makefile.am
+++ b/Makefile.am
@@ -117,7 +117,7 @@ include Makefrag.am
 include tests/Makefrag.am
 
 # Documentation.
-include doc/Makefrag.am
+#include doc/Makefrag.am
 
 #
 # Kernel Image