It's already always provided, and looks dangerous: it is mutated during
execution.

Noticed by Julien Muchembled.

Conflicts:
	stack/erp5/buildout.cfg
	stack/erp5/instance-erp5-cluster.cfg.in
	stack/erp5/instance-erp5-single.cfg.in
	stack/erp5/instance-kumofs.cfg.in
	stack/erp5/instance-zope.cfg.in
	stack/erp5/instance.cfg.in

Conflicts:
	component/libreoffice-bin/buildout.cfg

otherwise buggy slapos.core-1.0 will be used if exists.

running cp using slapos.core 1.0.0 in sr does not work.

because huBarcode 1.0.0 has an issue in importing PIL.