erp5_web_js_style: fix removal of local style property

Use the removeProperty method.
10 jobs for master in 0 seconds
Status Job ID Name Coverage
  External
passed ERP5.CodingStyleTest-Master

01:01:52

failed ERP5.PerformanceTest-Master

00:35:24

failed ERP5.UnitTest-Master

02:07:03

passed SlapOS.Eggs.UnitTest-Master.Python2

00:33:15

passed SlapOS.Eggs.UnitTest-Master.Python3

00:28:53

passed Wendelin.UnitTest-Master

00:34:02

passed SlapOS.Eggs.UnitTest-Master.Python2

00:23:30

passed SlapOS.Eggs.UnitTest-Master.Python2

00:23:24

passed SlapOS.Eggs.UnitTest-Master.Python3

00:37:04

passed SlapOS.Eggs.UnitTest-Master.Python3

00:25:36