segment: remove the bounds check from _to_running_time_full()

segment: remove the bounds check from _to_running_time_full()

Do not do any checks for the start/stop in the new
gst_segment_to_running_time_full() method, we can let this be done by
the more capable gst_segment_clip() method. This allows us to remove the
enum of results and only return the sign of the calculated running-time.
We need to put the old clipping checks in the old
gst_segment_to_running_time() still because they work slightly
differently than the _clip methods.

See https://bugzilla.gnome.org/show_bug.cgi?id=740575