credential: remove "Login" field on Person Credential view

There's not only one "login of a person", so it's better to show nothing
at all here.
7 jobs for arnau
Status Job ID Name Coverage
  External
failed ERP5.UnitTest-Master

03:39:13

passed SlapOS.Eggs.UnitTest-Master.Python2

00:45:03

passed SlapOS.Eggs.UnitTest-Master.Python3

00:16:00

failed ERP5.UnitTest-Master

failed ERP5.UnitTest-Master

02:04:20

failed SlapOS.Eggs.UnitTest-Master.Python2

passed SlapOS.Eggs.UnitTest-Master.Python3

00:18:18