update submodule libs/h5xx

* libs/h5xx 122ba9f...f7670aa (1):
  > support attributes of type std::vector<std::string>
utility/lua/hdf5: support string arrays as HDF5 attributes
mdsim.box: adjust to H5MD 1.0

Suppress output of box origin and write attribute on boundary conditions
as string array.

This commit refs #198804.
benchmark scripts: simplify construction of box

Pass space diagonal instead of list of edge vectors. Actually, HALMD
does not yet support non-cuboid boxes.