async: remove unused include directive

also remove the AARCH64_PORT_STUB which becomes useless.

Signed-off-by: Claudio Fontana <claudio.fontana@huawei.com>
aarch64: libc: remove unnecessary AARCH64_PORT_STUB

The stub implementation is not necessary anymore,
we have mmu and page faults now.

Signed-off-by: Claudio Fontana <claudio.fontana@huawei.com>