Remove extraneous parameters from hook_pre_contribution_create()

Having the function actually receive the parameters it is supposed to
receive somewhat increases the chance that it does what is supposed to
do, probably...
Fix retrieving of Creditor ID

Turns out the `creditor_id` in `civicrm_sdd_creditor` is a different
kind of Creditor ID than the Creditor ID we are looking for here. Fun,
ain't it?
XML: Fix typo in xsi declaration
XML: Add xsi:schemaLocation

No idea what this does; but the official example files have it -- so
probably a good idea to follow that...