Remove flow, not needed since karbon can do it all
Summary:
Since karbon is multipage app and stencils docker can be used by all apps,
there is no need for flow anymore.
Removing flow also 'fixes' problem with filter system, as it does not
know which app to open when two apps handle the same mimetype.
Test Plan: Tested with visio files.
Reviewers: anthonyfieroni
Subscribers: Calligra-Devel-list
Tags: #calligra:_3.0
Differential Revision: https://phabricator.kde.org/D25254