Fix memory leak when other players are riding a minecart

When a player jumps on a minecart, an mobj that shows where to jump on a minecart will spawn if you can jump in that direction. However, this arrow should only appear for the local player, so an additional check exists to make sure that arrow does not appear if you aren't the player riding the minecart. However, due to a miss in the game code, the logic for the right arrow incorrectly tries to remove the left arrow in this case, which causes the right arrow not to be removed from memory and thus leak.