Update git submodules

* Update helpcontent2 from branch 'master'
  - Refactor help page on empty cells
    
    Change-Id: I8bff8e56804fae90a71fb35c0a67b015356c2138
    Reviewed-on: https://gerrit.libreoffice.org/59585
    Tested-by: Jenkins
Reviewed-by: Olivier Hallot <olivier.hallot@libreoffice.org>
    

helpcontent2 @ ad2c3417

-Subproject commit 518f86fcc222c145c837f1e2e83e56128a30ed59
+Subproject commit ad2c3417d5a789ef775fdf70b85f7d95845d4d03