Description of problem:
this bug is found when verifing bug 1952744
enabled user workload monitoring and upgrade from 4.7.10 to 4.8.0-0.nightly-2021-05-10-225140
in 4.7.10 cluster, there is prometheus servicemonitor under openshift-user-workload-monitoring, since 4.8, prometheus servicemonitor is renamed to prometheus-user-workload, we should delete prometheus servicemonitor, but it still exists after upgrade to 4.8

NOTE: no functional effect in OpenShift cluster, since it reports "Error on ingesting samples with different value but same timestamp" in OSD cluster which bug 1952744 mentioned, we should remove the prometheus servicemonitor from openshift-user-workload-monitoring project

level=warn ts=2021-04-23T02:51:03.446Z caller=scrape.go:1375 component="scrape manager" scrape_pool=openshift-user-workload-monitoring/prometheus-user-workload/0 target=https://10.130.6.24:9091/metrics msg="Error on ingesting samples with different value but same timestamp" num_dropped=7
***********************************
# oc get clusterversion
NAME      VERSION   AVAILABLE   PROGRESSING   SINCE   STATUS
version   4.7.10    True        False         4m23s   Cluster version is 4.7.10

# oc -n openshift-user-workload-monitoring get servicemonitor
NAME                  AGE
prometheus            9m2s
prometheus-operator   9m18s
thanos-sidecar        9m2s
***********************************

after upgrade to 4.8.0-0.nightly-2021-05-10-225140
*************************************************
# oc -n openshift-user-workload-monitoring get servicemonitor
NAME                       AGE
prometheus                 71m
prometheus-operator        71m
prometheus-user-workload   29m
thanos-ruler               23m
thanos-sidecar             71m

# oc -n openshift-user-workload-monitoring get servicemonitor prometheus -oyaml
apiVersion: monitoring.coreos.com/v1
kind: ServiceMonitor
metadata:
  creationTimestamp: "2021-05-11T06:27:59Z"
  generation: 1
  labels:
    k8s-app: prometheus
  name: prometheus
  namespace: openshift-user-workload-monitoring
  resourceVersion: "29261"
  uid: 2e00db1d-e711-4d7c-bbae-9bb02edd18cd
spec:
  endpoints:
  - bearerTokenFile: /var/run/secrets/kubernetes.io/serviceaccount/token
    bearerTokenSecret:
      key: ""
    interval: 30s
    port: metrics
    scheme: https
    tlsConfig:
      ca: {}
      caFile: /etc/prometheus/configmaps/serving-certs-ca-bundle/service-ca.crt
      cert: {}
      serverName: prometheus-user-workload.openshift-user-workload-monitoring.svc
  namespaceSelector: {}
  selector:
    matchLabels:
      prometheus: user-workload

# oc -n openshift-user-workload-monitoring get servicemonitor prometheus-user-workload  -oyaml
apiVersion: monitoring.coreos.com/v1
kind: ServiceMonitor
metadata:
  creationTimestamp: "2021-05-11T07:10:02Z"
  generation: 1
  labels:
    app.kubernetes.io/component: prometheus
    app.kubernetes.io/name: prometheus
    app.kubernetes.io/part-of: openshift-monitoring
    app.kubernetes.io/version: 2.26.0
  name: prometheus-user-workload
  namespace: openshift-user-workload-monitoring
  resourceVersion: "47597"
  uid: 86f2236a-ec57-47a9-84e2-e85370e11e63
spec:
  endpoints:
  - bearerTokenFile: /var/run/secrets/kubernetes.io/serviceaccount/token
    bearerTokenSecret:
      key: ""
    interval: 30s
    port: metrics
    scheme: https
    tlsConfig:
      ca: {}
      caFile: /etc/prometheus/configmaps/serving-certs-ca-bundle/service-ca.crt
      cert: {}
      serverName: prometheus-user-workload.openshift-user-workload-monitoring.svc
  namespaceSelector: {}
  selector:
    matchLabels:
      app.kubernetes.io/component: prometheus
      app.kubernetes.io/name: prometheus
      app.kubernetes.io/part-of: openshift-monitoring
      prometheus: user-workload
*************************************************

Version-Release number of selected component (if applicable):
upgrade from 4.7.10 to 4.8.0-0.nightly-2021-05-10-225140

How reproducible:
always

Steps to Reproduce:
1. enabled user workload monitoring and upgrade from 4.7.10 to 4.8.0-0.nightly-2021-05-10-225140
oc adm upgrade --to-image=registry.ci.openshift.org/ocp/release:4.8.0-0.nightly-2021-05-10-225140 --allow-explicit-upgrade=true --force
2.
3.

Actual results:


Expected results:


Additional info: