arm64: drop unused __local_flush_icache_all()

After commit 65da0a8e ("arm64: use non-global mappings for UEFI
runtime regions"), nobody use __local_flush_icache_all() anymore,
so drop it.

Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>