Remove #include<boost/serialization/vector.hpp>. (#903)

The comments state the at some point boost serialization and
boost numeric had an ordering requirement of certain headers.

It claimed:

     // starting Boost 1.64, serialization header must come before ublas
     #include <boost/serialization/vector.hpp>
     #include <boost/numeric/ublas/matrix.hpp>

If this is still true then users must include the affected boost headers
before including `highfive/boost.hpp`. However, we're no longer forcing
the dependency onto all HighFive + Boost users.

include/highfive/boost.hpp

@@ -4,8 +4,6 @@
 #include "H5Exception.hpp"
 
 #include <boost/multi_array.hpp>
-// starting Boost 1.64, serialization header must come before ublas
-#include <boost/serialization/vector.hpp>
 #include <boost/numeric/ublas/matrix.hpp>
 
 namespace HighFive {