perf tools: Use just forward declarations for struct thread where possible

Removing various instances of unnecessary includes, reducing the maze of
header dependencies.

Link: http://lkml.kernel.org/n/tip-hwu6eyuok9pc57alookyzmsf@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/ui/browsers/hists.c

@@ -14,6 +14,7 @@
 #include "../../util/sort.h"
 #include "../../util/util.h"
 #include "../../util/top.h"
+#include "../../util/thread.h"
 #include "../../arch/common.h"
 
 #include "../browsers/hists.h"