Base class's 'Qt5FilePicker::cancel' already does nothing
just the same way.

Change-Id: Ie125d117f27849b29f082c72e320c1021e81163e
Reviewed-on: https://gerrit.libreoffice.org/68053
Tested-by: Jenkins
Reviewed-by: Katarina Behrens <Katarina.Behrens@cib.de>