Fix get property function for cohfar assignfar input-fname

Issue

While fixing compiler warnings, I came across a property that had issues. We make a gchar **input_fnames in cohfar_assignfar.c. It's parsed from a comma separated string which must have exactly 3 elements, the filepaths to our marginalized stats file for the given node/bank thingo.

As best I can tell, it was returning Just the first element, the 2w file, when get_property('input-fname') was called.
It was a little messy to figure out how to return it properly, and I couldn't find anywhere it was called, so I killed it.

Now gstreamer_python_upgrade returns a warning due to trying to access it, so Something, Somewhere is at least looping through all properties. It's probably best to make sure all our gstreamer element get/sets for properties work, even if we don't use them, so I've fixed it properly.

The offending commit: !65 (b5f2e87a)

Implementation

There may be a neater method than my join thingo that assumes 3 elements, but we've made that assumption elsewhere, and it'll likely be reworked in gstreamer python upgrade (the gchar stuff all seems a little deprecated.)

See https://www.freedesktop.org/software/gstreamer-sdk/data/docs/2012.5/glib/glib-String-Utility-Functions.html#g-strlcpy

Tests

It also builds and runs.