arm64/numa: remove some useless code

When the deleted code is executed, only the bit of cpu0 was set on
cpu_possible_mask. So that, only set_cpu_numa_node(0, NUMA_NO_NODE); will
be executed. And map_cpu_to_node(0, 0) will soon be called. So these code
can be safely removed.

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>