financial#152 remove determination of source

This function call determines the source, requiring quite a bit of complexity - however I believe it is unnecessary because either
1 ) we are completing an existing contribution - in which case the source will already exist or
2 ) we are repeating a contribution - in which case the source will be derived from the template contribution
(with recurring appended).

Removing this brings us close to the point where contribution is unnessary as an input parameter on the function