selftests: pidfd: drop needless linux/kcmp.h inclusion in pidfd_setns_test.c

kcmp is not used in pidfd_setns_test.c, so do not include <linux/kcmp.h>
Signed-off-by: Tommi Rantala <tommi.t.rantala@nokia.com>
Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

tools/testing/selftests/pidfd/pidfd_setns_test.c

@@ -16,7 +16,6 @@
 #include <unistd.h>
 #include <sys/socket.h>
 #include <sys/stat.h>
-#include <linux/kcmp.h>
 
 #include "pidfd.h"
 #include "../clone3/clone3_selftests.h"