Those files were split into validation.{cpp, h} and net_processing.{cpp, h}.
For lines that you have to change, many of them still exist just in different places. So you can use grep to search for them.
Thanks much!
I saw this series,
https://www.youtube.com/watch?v=mDGxGYvkDEEbut this is based on litecoin source version 0.8 (4 years ago version)
So there are many places to revise to make altcoin, are there no video or documents covering all the places needed to revise based on newest version?