remove dependency of imageio/ to stopwatch.h

Change-Id: I9b8e3909e97a26644b5ba6cbd9b29b8ef1727ba7
diff --git a/imageio/Makefile.am b/imageio/Makefile.am
index acabe67..d278a90 100644
--- a/imageio/Makefile.am
+++ b/imageio/Makefile.am
@@ -4,7 +4,6 @@
 noinst_HEADERS =
 noinst_HEADERS += ../src/webp/decode.h
 noinst_HEADERS += ../src/webp/types.h
-noinst_HEADERS += ../examples/stopwatch.h
 
 libimageio_util_la_SOURCES = imageio_util.c imageio_util.h