Eduplicate-p3dist-override

dh_python3 has an override mechanism (debian/py3dist-overrides) that lets you specify different prerequisites for particular Python imports.

debian/py3dist-overrides is mainly used for Python programs that use GObject introspection, since dh_python3 cannot yet detect that the packages gir1.2-- map to Python imports, so overrides are needed.

When the same import appears twice in the file, the information from the first one is used but all the others are discarded. That can lead to missing prerequisites.

An example of a second line that gets ignored:

gi.repository.Gst gir1.2-gst-plugins-base-1.0
gi.repository.Gst gir1.2-gstreamer-1.0

An example of a double dependency that gets kept:

gi.repository.Gst gir1.2-gst-plugins-base-1.0, gir1.2-gstreamer-1.0

Refer to Bug#980987 for details.