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/builtin-inject.c

@@ -18,6 +18,7 @@
 #include "util/data.h"
 #include "util/auxtrace.h"
 #include "util/jit.h"
+#include "util/thread.h"
 
 #include <subcmd/parse-options.h>