drop readerr

src/cmd/jpg/readpng.c

diff --git a/src/cmd/jpg/readpng.c b/src/cmd/jpg/readpng.c
index 9392f07..f6e8e9d 100644
--- a/src/cmd/jpg/readpng.c
+++ b/src/cmd/jpg/readpng.c
@@ -46,7 +46,6 @@
 
 static ulong *crctab;
 static uchar PNGmagic[] = {137,80,78,71,13,10,26,10};
-static char readerr[] = "ReadPNG: read error: %r";
 static char memerr[] = "ReadPNG: malloc failed: %r";
 
 static ulong