fix with recent boost https://github.com/ledger/ledger/pull/2337

Index: src/system.hh.in
--- src/system.hh.in.orig
+++ src/system.hh.in
@@ -144,7 +144,6 @@
 #include <boost/date_time/posix_time/posix_time_io.hpp>
 #include <boost/date_time/gregorian/gregorian_io.hpp>
 
-#include <boost/filesystem/convenience.hpp>
 #include <boost/filesystem/exception.hpp>
 #include <boost/filesystem/fstream.hpp>
 #include <boost/filesystem/operations.hpp>
