Update git submodules

* Update helpcontent2 from branch 'master'
  - Stop index headers from being linkified
    
    Change-Id: If445b693feb17fd943eced3a222a20b26039891d
    Reviewed-on: https://gerrit.libreoffice.org/63759
    Tested-by: Jenkins
Reviewed-by: Jan-Marek Glogowski <glogow@fbihome.de>
Reviewed-by: Olivier Hallot <olivier.hallot@libreoffice.org>
    

helpcontent2 @ a678c053

-Subproject commit 07d6d9548446b022fe319b898bf7ab6f64f7ed98
+Subproject commit a678c05324cff46eace7c439a4595a3014fa8576