perf tools: Remove string.h, unistd.h and sys/stat.h from util.h

Not needed in this header, added to the places that need FILE,
putchar(), access() and a few other prototypes.

Link: http://lkml.kernel.org/n/tip-xxtdsl6nsna82j7puwbdjqhs@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-help.c

@@ -14,6 +14,10 @@
 #include "util/debug.h"
 #include <linux/kernel.h>
 #include <errno.h>
+#include <stdio.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <unistd.h>
 
 static struct man_viewer_list {
 	struct man_viewer_list *next;