I don’t have the functions_db.php file in my 2.04 instalation. I think the file don’t came with setup and I don’t have it.
That file has been included in the kiwitrees/includes/ folder of kiwitrees since before version 1.4.4 (first edition). It was also in the same place before that in webtrees, and before that in PGV. It has never “not” been part of the package. If it is not there now in your version of 2.0.4 then it has been deleted at your end. No version of kiwitrees (ever) would work without it.
But I no longer have any copies of versions as old as that, so cannot supply a copy.