Drop all gnc-module dependencies and includes from compilation units that no longer use it

This also drops the python wrapper for gnc-module. As for the guile wrappers,
python should use other means of loading our shared libraries.

This commit required a few tweaks to the dependency chain as some units
inherited dependency information from gnc-module's public dependency
interface.

libgnucash/backend/xml/test/test-load-example-account.cpp

@@ -32,7 +32,6 @@ extern "C"
 #include <unistd.h>
 #include <dirent.h>
 
-#include "gnc-module.h"
 #include "gnc-engine.h"
 #include "test-engine-stuff.h"
 }

libgnucash/backend/xml/test/test-xml-commodity.cpp

@@ -26,7 +26,6 @@ extern "C"
 #include <stdlib.h>
 #include <unistd.h>
 
-#include "gnc-module.h"
 #include "qof.h"
 #include "test-engine-stuff.h"