Remove name prefix from default kustomization

The name prefix is already present in the manager (operator)
kustomization. Adding it here would produce doubly prefixed names e.g.
rabbitmq-cluster-rabbitmq-cluster-operator

Author: Zerpet

Diff for: config/default/base/kustomization.yaml

@@ -9,7 +9,6 @@ apiVersion: kustomize.config.k8s.io/v1beta1
 kind: Kustomization
 
 namespace: rabbitmq-system
-namePrefix: rabbitmq-cluster-
 resources:
 - ../../manager
 # [CERTMANAGER] Uncomment next line to enable cert-manager