How do I remove the easter egg Morte mod?

You'll need to delete all the mod's files from the game's override directory.

I don't need to reinstall any files the mod may have replaced?

I don't think the mod overwrites any files originally there. The readme (which also has the [un]install information) doesn't mention anything being overwritten.

It does not override any existing files in the override folder.

It does "replace" some files in the BIF files (actual files with all the data), by beeing in the override folder, so just deleting the file in override makes the game use the old files from the BIF files again.