msi: LibreOffice does not use SystemFolder, don't define it

LibreOffice does not install anything into SystemFolder (i.e. into
C:\WINDOWS\SYSTEM32 or similar). However, merge module of MS VC++
Runtime does. And if SystemFolder defined in MSM is different than
SystemFolder defined in base MSI, then a conflict will occur, and
merge will fail.

Change-Id: I33649babcd33575aa17cd0e3c0ab612a81ceec98