kselftest:sched: remove duplicate include in cs_prctl_test.c

Clean up the following includecheck warning:

./tools/testing/selftests/sched/cs_prctl_test.c:
Include files sys/types.h and sys/wait.h are included more than
once.

No functional change.

Fixed commit header and log:
Shuah Khan <[e-mail]>

Reported-by: Zeal Robot <[e-mail]>
Signed-off-by: Changcheng Deng <[e-mail]>
Signed-off-by: Shuah Khan <[e-mail]>

tools/testing/selftests/sched/cs_prctl_test.c

···
 #include <sys/types.h>
 #include <sched.h>
 #include <sys/prctl.h>
-#include <sys/types.h>
-#include <sys/wait.h>
 #include <unistd.h>
 #include <time.h>
 #include <stdio.h>