slapos_cloud: drop source_administration on Compute Node

master/bt5/slapos_cloud/WorkflowTemplateItem/portal_workflow/compute_node_slap_interface_workflow/script_ComputeNode_approveRegistration.py

 compute_node = state_change['object']
 portal = compute_node.getPortalObject()
-person = portal.portal_membership.getAuthenticatedMember().getUserValue()
 compute_node.edit(
-  source_administration_value=person,
   upgrade_scope='auto',
   capacity_scope='open'
 )