Many OpenType features are required features that are applied to certain
context determined by the layout engine, or should always be on. There
is no value in presenting these features to the user and they just
clutter the dialog for fonts that usually have many of such features
(e.g. Arabic or Indic fonts).

Change-Id: Idc3d7d3a9eb1c4f693ea6fdf9f26f0264b910f91
Reviewed-on: https://gerrit.libreoffice.org/55951
Tested-by: Jenkins
Reviewed-by: Tomaž Vajngerl <quikee@gmail.com>