To answer your question: There is no rule regarding this, which is why you can't find the answer! If you want an even number of turns thenwith: 72 basic tiles, you should remove 2 randomly selected ones. This leaves 23 tiles per player and the starting tile. This would be how you should play for even turns.
Mind you it really does not matter or affect the game that much, but if you want to get 'competition' style playing then by all means remove the tiles.
However, if you use Traders and Builders, the builder, due to the double-turn, makes it impossible for each player to get an even number of turns without having to keep fine track of them.
Hope this helps.
Thanks for the quick answer!