selftests: Remove unneeded selftest API headers

Remove unused includes of the kselftest.h header.

Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

tools/testing/selftests/pidfd/pidfd_getfd_test.c

@@ -18,7 +18,6 @@
 #include <linux/kcmp.h>
 
 #include "pidfd.h"
-#include "../kselftest.h"
 #include "../kselftest_harness.h"
 
 /*

tools/testing/selftests/pidfd/pidfd_setns_test.c

@@ -20,7 +20,6 @@
 
 #include "pidfd.h"
 #include "../clone3/clone3_selftests.h"
-#include "../kselftest.h"
 #include "../kselftest_harness.h"
 
 enum {