perf tools: Add signal.h to places using its definitions

And remove it from util.h, disentangling it a bit more.

Link: http://lkml.kernel.org/n/tip-2zg9s5nx90yde64j3g4z2uhk@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/ui/gtk/annotate.c

@@ -4,6 +4,7 @@
 #include "util/evsel.h"
 #include "ui/helpline.h"
 #include <inttypes.h>
+#include <signal.h>
 
 enum {
 	ANN_COL__PERCENT,

tools/perf/ui/gtk/hists.c

@@ -6,6 +6,7 @@
 #include "../helpline.h"
 #include "../string2.h"
 #include "gtk.h"
+#include <signal.h>
 
 #define MAX_COLUMNS			32