cleanup: fix include order

When touching a file, the linter also complains about the order of includes
that existed before. To make the linter happy, reorder the includes
accordingly.

Author: nmanthey

src/goto-instrument/reachability_slicer.cpp

@@ -17,10 +17,10 @@ Author: Daniel Kroening, [email protected]
 
 #include <stack>
 
+#include <goto-programs/cfg.h>
 #include <goto-programs/remove_calls_no_body.h>
 #include <goto-programs/remove_skip.h>
 #include <goto-programs/remove_unreachable.h>
-#include <goto-programs/cfg.h>
 
 #include "util/message.h"