Use upstream Magnum

Our downstream Magnum was for keeping Heat driver support.
But we dropped them, so there's no need to build magnum from downstream.

Author: seunghun1ee

etc/kayobe/kolla.yml

@@ -139,10 +139,6 @@ kolla_sources:
     type: git
     location: https://github.com/stackhpc/keystone.git
     reference: stackhpc/{{ openstack_release }}
-  magnum-base:
-    type: git
-    location: https://github.com/stackhpc/magnum.git
-    reference: stackhpc/{{ openstack_release }}
   neutron-server-plugin-networking-mlnx:
     type: git
     location: https://github.com/stackhpc/networking-mlnx.git