erp5_xhtml_style: fixup: do not index xhtml style by default

See merge request !1510
6 jobs for master in 0 seconds
Status Job ID Name Coverage
  External
passed ERP5.CodingStyleTest-Master

00:47:39

failed ERP5.UnitTest-Master

01:34:46

failed ERP5.UnitTest-Master.Medusa

01:52:35

passed SlapOS.Eggs.UnitTest-Master.Python2

passed SlapOS.Eggs.UnitTest-Master.Python3

00:12:53

passed SlapOS.Eggs.UnitTest-Master.Python2

00:09:42