[IMP] ir.model.data: remove obsolete _unlink() and unlink_mark, and their references
[IMP] ir.model.data: remove obsolete _unlink() and unlink_mark, and their references

Now all deletions in ir.model.data are automatically handled by ORM 
during the regular call to orm.unlink(). No need for any manual care.
splbio/openobject-server,vnc-biz/openerp-server,ovnicraft/openerp-server,gisce/openobject-server,vnc-biz/openerp-server,ovnicraft/openerp-server,MarkusTeufelberger/openobject-server,gisce/openobject-server,splbio/openobject-server,MarkusTeufelberger/openobject-server,splbio/openobject-server,gisce/openobject-server,MarkusTeufelberger/openobject-server