update release notes for EasyBuild v1.16.0

there never was an `mpif90.h`, only `mpif.h`, but I guess you're referring to the `libmpi_f90.so` no longer being there for recent OpenMPI versions.

That's normal, since they've revamped the Fortran MPI binding in OpenMPI v1.7, cfr. http://www.open-mpi.org/community/lists/announce/2013/04/0053.php. 

There now only is `libmpi_mpifh.so`, which replaces `libmpi_f77.so` and `libmpi_f90.so`...