media: let the source unref the last media ref
media: let the source unref the last media ref

the last ref to the media is held by the source so we don't need to add more ref
and unrefs, we simply destroy the media when the source is gone.

thaytan/gst-rtsp-server,hsteinhaus/gst-rtsp-server,surround-io/gst-rtsp-server,Lachann/gst-rtsp-server,barisdemiray/gst-rtsp-server,barisdemiray/gst-rtsp-server,Lachann/gst-rtsp-server,hsteinhaus/gst-rtsp-server,surround-io/gst-rtsp-server,barisdemiray/gst-rtsp-server,thaytan/gst-rtsp-server,surround-io/gst-rtsp-server,hsteinhaus/gst-rtsp-server,thaytan/gst-rtsp-server,Lachann/gst-rtsp-server