rtp: opuspay: fix memory leak in gst_rtp_opus_pay_setcaps.
rtp: opuspay: fix memory leak in gst_rtp_opus_pay_setcaps.

The src caps were never dereferenced, causing a memory leak.

GStreamer/gst-plugins-good,GStreamer/gst-plugins-good,GStreamer/gst-plugins-good,pexip/gst-plugins-good,pexip/gst-plugins-good,GStreamer/gst-plugins-good,pexip/gst-plugins-good,pexip/gst-plugins-good,pexip/gst-plugins-good