fix(core): disable C assert in upstream keepalive patch

[chronolaw]

Summary

See: KAG-474

Core code:

upool = lua_newuserdata(L, size); /* pools upool */

items = (ngx_http_lua_balancer_keepalive_item_t *) (&upool->free + 1);

ngx_http_lua_assert((void *) items == ngx_align_ptr(items, NGX_ALIGNMENT));

items points to the memory that allocated by LuaJIT (lua_newuserdata),
so it may not fit the Nginx's alignment requirement.

Checklist

• The Pull Request has tests
• There's an entry in the CHANGELOG
• There is a user-facing docs PR against https://github.com/Kong/docs.konghq.com - PUT DOCS PR HERE

[dndx]

We should remove this unneeded code, instead of commenting it out. It is a good habit to have.