matroska: remove useless check

No need to check for context availability while freeing. We are inside
inside a code block with a condition that dereferences context.
if (context->type == 0 ...

https://bugzilla.gnome.org/show_bug.cgi?id=751306

gst/matroska/matroska-demux.c

@@ -1123,9 +1123,7 @@ gst_matroska_demux_add_stream (GstMatroskaDemux * demux, GstEbmlRead * ebml)
     demux->common.num_streams--;
     g_ptr_array_remove_index (demux->common.src, demux->common.num_streams);
     g_assert (demux->common.src->len == demux->common.num_streams);
-    if (context) {
-      gst_matroska_track_free (context);
-    }
+    gst_matroska_track_free (context);
 
     return ret;
   }

gst/matroska/matroska-parse.c

@@ -940,9 +940,7 @@ gst_matroska_parse_add_stream (GstMatroskaParse * parse, GstEbmlRead * ebml)
     parse->common.num_streams--;
     g_ptr_array_remove_index (parse->common.src, parse->common.num_streams);
     g_assert (parse->common.src->len == parse->common.num_streams);
-    if (context) {
-      gst_matroska_track_free (context);
-    }
+    gst_matroska_track_free (context);
 
     return ret;
   }