Portion of diff was dropped in the mappings update commit.
Also remove the option to remove invalid statistics. The server will
automatically do this now as of... 1.13?, our option wasn't even doing anything.
Say a player shoots an arrow through a nether portal, the game
would lose the shooter for determining things such as Player Kills,
because the entity is in another world.
If the projectile fails to find the shooter in the current world, check
other worlds.