selftests/seccomp: Remove syscall setting #ifdefs

With all architectures now using the common SYSCALL_NUM_SET() macro, the
arch-specific #ifdef can be removed from change_syscall() itself.

Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/lkml/20200912110820.597135-8-keescook@chromium.org


Acked-by: Christian Brauner <christian.brauner@ubuntu.com>