wb: prevent unit id conflics

the wb recruit actions store temp units with fake ids and live longer
than a turn, so resetting the underlying id counter between turns might
result in dublicate id errors in wb recruit actions ( #1517 ), which
might lead to errors later.

With this it is of course possible to get erros when more than 2^31 (or
2^63 on a 64 bit wesnoth version.) fake units are generated during a
game, but that is less likely.

(cherry-picked from commit 775f3ec995)

src/play_controller.cpp

@@ -553,7 +553,6 @@ void play_controller::finish_side_turn()
 	}
 
 	mouse_handler_.deselect_hex();
-	resources::gameboard->unit_id_manager().reset_fake();
 	gamestate_->init_side_done() = false;
 }