vcl/source/window/wrkwin.cxx: drop unused svsys.h header

Change-Id: Iad99721f6026512584c6e1cb763b81ffc6d1a625
Reviewed-on: https://gerrit.libreoffice.org/10152
Tested-by: LibreOffice gerrit bot <gerrit@libreoffice.org>
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>