Remove instantiation of transaction from payment express ipn class

[eileenmcnaughton]

Overview
Minor code cleanup

Before

PaymentExpressIPN calls parent::completeTransaction

After

PaymentExpressIPN calls the function that the parent calls, without needlessly instantiating the transaction

Technical Details

This class is hopefully unused, however, this change should be safe regardless as it just calls the same function
without needlessly instantiating the transaction

Note this processor is not enabled on install or recommended

Comments

[civibot]

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