Remove extra /head html element

This probably affects google dataset search because the corresponding dataset structure is currently found outside of the html element as indicated here https://search.google.com/structured-data/testing-tool/u/0/#url=https%3A%2F%2Fdoi.org%2F10.15151%2Fesrf-es-58784441

This is also causing errors on the html editor https://validator.w3.org/nu/?doc=https%3A%2F%2Fdoi.esrf.fr%2F10.15151%2FESRF-ES-58784441