text: Title: Add-On manager should not be creating kube-system namespace
  Body: **What happened**:
  Add-on manager uses kubectl apply to create the kube-system namespace at start-up. 
  This is redundant because the kube-apiserver creates the namespace in NewBootstrapController. 
  This is a problem because if someone uses apply to make changes to the kube-system namespace, the add-on manager will wipe out these changes. 
  
  **What you expected to happen**:
  Kube-APIServer has the sole responsibility of creating the kube-system namespace.
  
  **How to reproduce it (as minimally and precisely as possible)**:
  kubectl apply a label to the kube-system namespace.
  restart the add-on manager.
  Note the labels have been removed.
  
  **Anything else we need to know?**:
  /sig api-machinery
  
  **Environment**:
  - Kubernetes version (use `kubectl version`):
  - Cloud provider or hardware configuration:
  - OS (e.g: `cat /etc/os-release`):
  - Kernel (e.g. `uname -a`):
  - Install tools:
  - Others:
  