erp5_travel_expense: remove leaves days counter

See merge request !1505
9 jobs for master in 0 seconds
Status Job ID Name Coverage
  External
passed ERP5.CodingStyleTest-Master

00:56:06

passed ERP5.PerformanceTest-Master

00:24:30

failed ERP5.UnitTest-Master

01:30:52

failed ERP5.UnitTest-Master.Medusa

02:00:59

passed SlapOS.Eggs.UnitTest-Master.Python2

00:10:57

passed SlapOS.Eggs.UnitTest-Master.Python3

01:26:35

failed ERP5.UnitTest-Master

01:33:56

passed SlapOS.Eggs.UnitTest-Master.Python2

00:11:28

passed SlapOS.Eggs.UnitTest-Master.Python3

00:20:22