BTreeFolder2: Disable manage_delAllObjects

Protect data from human error. There are unbelievable mistakes. ERP5
is a place to store important data that must not be deleted easily.
7 jobs for master in 0 seconds
Status Job ID Name Coverage
  External
passed ERP5.CodingStyleTest-Master

01:14:09

passed ERP5.PerformanceTest-Master

00:26:52

failed ERP5.UnitTest-Master

01:54:54

failed ERP5.UnitTest-Zope2

03:48:34

passed SlapOS.Eggs.UnitTest-Master.Python2

00:13:17

passed SlapOS.Eggs.UnitTest-Master.Python3

00:17:12

passed Wendelin.UnitTest-Master

03:37:36