std/png: delete old comment re APNG is unsupported
diff --git a/std/png/README.md b/std/png/README.md
index 75a3842..5b34706 100644
--- a/std/png/README.md
+++ b/std/png/README.md
@@ -5,8 +5,6 @@
 PNG](https://wiki.mozilla.org/APNG_Specification)) is an unofficial extension
 for animated images.
 
-Wuffs does not currently implement the APNG extension.
-
 
 ## File Structure