Revert "CoreAPI getRelationships now delegates to kernel API."

This reverts commit e8043a30c78f88a75a5e0c106bd2d18356612adb.
due to heavy performance hit. Will make its way in at a later point.
Revert "Initial work on listing rels for a node via kernel API."

This reverts commit 81d75c3419560abea0e6333e43341168f31ff218.