ext/: Don't take the stream lock.

ext/: Don't take the stream lock.

Original commit message from CVS:
2005-11-21  Andy Wingo  <wingo@pobox.com>

* ext/sidplay/gstsiddec.cc (gst_siddec_sink_event):
* ext/mpeg2dec/gstmpeg2dec.c (gst_mpeg2dec_sink_event):
* ext/mad/gstmad.c (gst_mad_sink_event):
* ext/a52dec/gsta52dec.c (gst_a52dec_sink_event): Don't take the
stream lock.

* gst/realmedia/rmdemux.c (gst_rmdemux_perform_seek): Update for
stream lock changes.