LibreOffice-still is a virtual package not present in Sisyphus
(only in P11). Remove its list and group files entirely.

In libreoffice-latest list, replace virtual package names with real
ones (LibreOffice -> libreoffice, LibreOffice-langpack-ru ->
libreoffice-langpack-ru, LibreOffice-gtk3 -> libreoffice-gtk3).
Remove LibreOffice-common (provided by libreoffice).

Rename installer group to "Офисный пакет LibreOffice" and set
Required=yes (enabled by default).