rtsp-media: Strip keys from the fmtp that we use internally in our caps
rtsp-media: Strip keys from the fmtp that we use internally in our caps

Skip keys from the fmtp, which we already use ourselves for the
caps. Some software is adding random things like clock-rate into
the fmtp, and we would otherwise here set a string-typed clock-rate
in the caps... and thus fail to create valid RTP caps

https://bugzilla.gnome.org/show_bug.cgi?id=753009

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