bpf: lru: Remove unused declaration bpf_lru_promote()

Commit 3a08c2fd ("bpf: LRU List") declared but never implemented this.

Signed-off-by: Yue Haibing <yuehaibing@huawei.com>
Link: https://lore.kernel.org/r/20230808145531.19692-1-yuehaibing@huawei.com


Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>