[devel] Revise references to zlib/libpng license

pngtrans.c

diff --git a/pngtrans.c b/pngtrans.c
index b7adb14..ae551b5 100644
--- a/pngtrans.c
+++ b/pngtrans.c
@@ -7,7 +7,7 @@
  * (Version 0.88 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.)
  *
  * This code is released under the zlib/libpng license.
- * For conditions of distribution and use, see copyright notice, disclaimer,
+ * For conditions of distribution and use, see the disclaimer
  * and license in png.h
  */