rhbz#1105376 move FlatODF filter config to right place

This has been broken since 3.3(!), when the old XSLT based import/export
was replaced by a library.

Change-Id: Id335f296c5a0e2c15d1748f8a14ac8d4001e1d15
(cherry picked from commit 6e299a555dc03982f6e03434f2726ca440fcee53)
Reviewed-on: https://gerrit.libreoffice.org/9691
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>