Update references to decodebin

Update old references for decodebin2 to decodebin.
diff --git a/gst/videoparsers/gsth265parse.c b/gst/videoparsers/gsth265parse.c
index 86f4f7a..896b7e8 100644
--- a/gst/videoparsers/gsth265parse.c
+++ b/gst/videoparsers/gsth265parse.c
@@ -320,7 +320,7 @@
   caps = gst_pad_get_allowed_caps (GST_BASE_PARSE_SRC_PAD (h265parse));
   GST_DEBUG_OBJECT (h265parse, "allowed caps: %" GST_PTR_FORMAT, caps);
 
-  /* concentrate on leading structure, since decodebin2 parser
+  /* concentrate on leading structure, since decodebin parser
    * capsfilter always includes parser template caps */
   if (caps) {
     caps = gst_caps_truncate (caps);