The version of Kustomize in Flux does not handle $patch: delete correctly and needs to be upgraded

[Crayeth]

Using

image:
  repository: docker.io/fluxcd/flux
  tag: 1.20.1

I've found that the Kustomize therein included (3.7.0) does not render patches with $patch: delete correctly.
If I have something like:

external_services:
  grafana:
    $patch: delete

I expect grafana and everything belonging to it to be deleted but it is not.
Using Kustomize 3.8.2 locally does render correctly.

[stefanprodan]

Fixed in #3309