accrual: Remove the consistency checker.

Everything it said was a problem has been done legitimately in our books at
one point or another.

* Variation in contract can happen in different line items of an invoice or
"group of contractor" situations.

* Variation in cost can happen because one invoice spans a period of time,
like donation matching programs. There is probably still value in a tool
that checks to make sure we use consistent rates each day, but that
affects all kinds of transactions, not just accruals, so it would be
done better in a separate tool.

* Variation in account happens because invoices legitimately span accrual
accounts, like donation matching programs with fees payable.

So: it's gone, good riddance.