test/rtp_decoder.c: Removed superfluous conditional

No need to check the same thing twice! Re issue #158
diff --git a/test/rtp_decoder.c b/test/rtp_decoder.c
index 3410791..f4823cf 100644
--- a/test/rtp_decoder.c
+++ b/test/rtp_decoder.c
@@ -441,7 +441,7 @@
   srtp_err_status_t status;
   dcdr->frame_nr++;
 
-  if (dcdr->start_tv.tv_sec == 0 && dcdr->start_tv.tv_sec == 0) {
+  if (dcdr->start_tv.tv_sec == 0) {
     dcdr->start_tv = hdr->ts;
   }