help request: remove useless code

[nic-chen]

Description

These lines of code (https://github.com/apache/apisix/blob/master/apisix/utils/log-util.lua#L359-L361) are meaningless and have no effect, because before core.response.hold_body_chunk is executed, ctx._resp_body_bytes is nil and will not continue to execute and return.

Environment

• APISIX version (run apisix version): master
• Operating system (run uname -a):
• OpenResty / Nginx version (run openresty -V or nginx -V):
• etcd version, if relevant (run curl http://127.0.0.1:9090/v1/server_info):
• APISIX Dashboard version, if relevant:
• Plugin runner version, for issues related to plugin runners:
• LuaRocks version, for installation issues (run luarocks --version):