selftests/powerpc: Remove duplicate header

Remove duplicate headers which are included twice.

Signed-off-by: Sabyasachi Gupta <sabyasachi.linux@gmail.com>
Signed-off-by: Souptick Joarder <jrdr.linux@gmail.com>
[mpe: Split out of larger patch]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

tools/testing/selftests/powerpc/pmu/ebb/fork_cleanup_test.c

@@ -11,7 +11,6 @@
 #include <sys/wait.h>
 #include <unistd.h>
 #include <setjmp.h>
-#include <signal.h>
 
 #include "ebb.h"