livepatch: Remove redundant copy for old codes

hulk inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I53WZ9



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Before commit ec7ce700674f ("[Huawei] livepatch: put memory alloc and
free out stop machine"), procedure of restore codes of old function in
'arch_klp_unpatch_func' is like:
  1. copy old codes which saved in func_node into array 'old_insns';
  2. free memory of func_node;
  3. patch text with old codes in array 'old_insns';

But after above commit, operation of freeing memory of func_node in
procedure 2 is done after 'arch_klp_unpatch_func' succeed. And then
operation of copying old codes in procedure 1 seems redundant, so we
can just remove it.

Suggested-by: Xu Kuohai <xukuohai@huawei.com>
Signed-off-by: Zheng Yejian <zhengyejian1@huawei.com>
Reviewed-by: Kuohai Xu <xukuohai@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>