Refactor: tools: Don't use g_propagate_error in reconcile_output_formats

We don't need a local error and g_propagate_error(). That's for cases
where "the sub-function does not indicate errors other than by
reporting a GError." The callbacks all return gboolean result codes
(which happen to be always TRUE, since no error can occur without an
assertion). See https://docs.gtk.org/glib/error-reporting.html.

Also add doxygen

Signed-off-by: Reid Wahl <nrwahl@protonmail.com>