Update git submodules

* Update helpcontent2 from branch 'master'
  - Height and width are <img> attributes
    
    Change-Id: Ia8084ff7029ddd06e450cbf03a7b1fb5efaa7dc7
    Reviewed-on: https://gerrit.libreoffice.org/60136
    Tested-by: Jenkins
Reviewed-by: Olivier Hallot <olivier.hallot@libreoffice.org>
    

helpcontent2 @ 991e7f1f

-Subproject commit 975365445280e10d567dfb0bd8be6e5eb1dfdc46
+Subproject commit 991e7f1f76d5ff87373cdf6e9f74897f36d8c393