[FIX] hr_payroll: total_wage return format

Field removed in 9.0 at 04cebbd5 (because useless). This avoids an error if read.
cf #8781

addons/hr_payroll/hr_payroll.py

@@ -975,7 +975,7 @@ class hr_employee(osv.osv):
         current_date = datetime.now().strftime('%Y-%m-%d')
         for employee in self.browse(cr, uid, ids, context=context):
             if not employee.contract_ids:
-                res[employee.id] = {'basic': 0.0}
+                res[employee.id] = 0.0
                 continue
             cr.execute( 'SELECT SUM(wage) '\
                         'FROM hr_contract '\
@@ -984,7 +984,7 @@ class hr_employee(osv.osv):
                         'AND (date_end > %s OR date_end is NULL)',
                          (employee.id, current_date, current_date))
             result = dict(cr.dictfetchone())
-            res[employee.id] = {'basic': result['sum']}
+            res[employee.id] = result['sum']
         return res
 
     _columns = {