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>
diff --git a/tools/perf/perf.c b/tools/perf/perf.c
index 0b2cad0..4cc6960 100644
--- a/tools/perf/perf.c
+++ b/tools/perf/perf.c
@@ -24,6 +24,9 @@
 #include <signal.h>
 #include <stdlib.h>
 #include <time.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <unistd.h>
 #include <linux/kernel.h>
 
 const char perf_usage_string[] =