Fix documentation example error for checkout session mode

[edgarlr]

Currently, the checkout session mode example has a type error in the documentation, if you set cartMode="checkout-session" then mode="payment" does not exist in type

That behavior is expected since the mode and other parameters are defined in the backend and the CheckoutSession mode doesn't actually include the mode

https://github.com/dayhaysoos/use-shopping-cart/blob/f3bd4736916c4bf97c0c7cd8af6a25d4a8ab87d8/use-shopping-cart/core/index.d.ts#L58-L63

So the is only remove that line from the example

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