lib9/utf: Remove superfluous header inclusion.

<stdint.h> does not seem to be needed.

R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/8178044

src/lib9/utf/utf.h

@@ -16,8 +16,6 @@
 #ifndef _UTFH_
 #define _UTFH_ 1
 
-#include <stdint.h>
-
 typedef unsigned int Rune;	/* Code-point values in Unicode 4.0 are 21 bits wide.*/
 
 enum