stack/erp5: reorder [versions] priority.

1) stack/erp5/zope-versions.cfg
2) stack/slapos.cfg
3) component/ZODB/buildout.cfg.

and remove stack/erp5/ztk-versions.cfg as we need only small part of it.
Status Job ID Name Coverage
  External
passed ERP5.CodingStyleTest-Zope4Py2

01:31:05

failed ERP5.UnitTest-Zope4Py2

01:41:15

failed SlapOS-Master.UnitTest-Zope4py2

01:56:20

passed SlapOS.SoftwareReleases.IntegrationTest-Zope4Py2

05:42:05

failed SlapOS-Master.UnitTest-Zope4py2

01:18:04

failed SlapOS-Master.UnitTest-Zope4py2

02:25:19

failed SlapOS-Master.UnitTest-Zope4py2

01:11:07

canceled SlapOS-Master.UnitTest-Zope4py2

01:16:40

failed SlapOS-Master.UnitTest-Zope4py2

02:13:32

failed SlapOS-Master.UnitTest-Zope4py2

01:14:05

failed SlapOS-Master.UnitTest-Zope4py2

01:14:52

canceled SlapOS-Master.UnitTest-Zope4py2

01:19:49

failed SlapOS-Master.UnitTest-Zope4py2

01:52:32

failed SlapOS-Master.UnitTest-Zope4py2

01:18:09

failed SlapOS-Master.UnitTest-Zope4py2

02:14:07