Weaken the python3 bindings base package dependency for modular builds
Different parts of libreports are built and shipped with
different modules in F26 Boltron, namely modules/shared-userspace
and modules/dnf. This allows libreport-python3 from modules/dnf
work with libreport from modules/shared-userspace even though
they have different dist tags.
This only affects modularity builds and shouldn't be needed
beyond F26 Boltron.
Signed-off-by: Petr Šabata <contyk@redhat.com>