Remove eel_ref_str in favor of GRefString
Atomically reference counted strings API has been added to GLib last cycle: https://www.bassi.io/articles/2018/09/04/ref-counting/
This can replace the eel_ref_str
API found in eel/eel-string.[c,h].
Reference documentation here: https://developer.gnome.org/glib/stable/glib-Reference-counted-strings.html