project_billing_utils: dissociate invoice wizard uses SQL and that breaks triggers in module analytic_hours_block

To reproduce:

in 7.0, install analytic_hours_block in and project_billing_utils.

- Create an invoice with a analytic account and confirm it.
- create an hour block associated to the invoice.
- create an analytic line on the same analytic account, analytic journal of type General (i.e. Timesheet Journal).
- Use the Associate wizard introduced in project_billing_utils to associate it to the block.
- Check that in the hour block the time spent is updated.
- Now use the Dissociate wizard, again from project_billing_utils to dissociate the line from the block
- Check in the block: the line is still counted as worked.

Thanks