fix(cash): remove fault SQL exception handlers

This commit removes problematic SQL exception handlers from the
CalculateCashInvoiceBalances() stored procedure.  All exception handling
should be done with the `db.transaction()` framework ... having these
extra handler in the SQL code led to confusing error messages when
strict mode throws exceptions.

With these exceptions removed, and the Vanga database re-created, the
issues posting USD cash payments disappears.

Closes Third-Culture-Software#1445.

server/models/procedures.sql

@@ -839,9 +839,6 @@ BEGIN
   DECLARE enterpriseCurrencyId INT;
   DECLARE currentExchangeRate DECIMAL(19,4);
 
-  DECLARE EXIT HANDLER FOR SQLEXCEPTION ROLLBACK;
-  DECLARE EXIT HANDLER FOR SQLWARNING ROLLBACK;
-
   -- copy cash payment values into working variables
   SELECT cash.date, cash.currency_id, enterprise.id, enterprise.currency_id, cash.debtor_uuid
     INTO cashDate, cashCurrencyId, cashEnterpriseId, enterpriseCurrencyId, cashDebtorUuid