Description of problem: Storageclass conversion plans have migstorage reference even though it's not being used. Storageclass conversion plan shouldn’t have migstorage reference.

Version-Release number of selected component (if applicable):
MTC 1.7.1


How reproducible:
Always

Steps to Reproduce:
1. Create a migplan with migration_type as storage class conversion from UI

Actual results: Migplan has a migstorage reference. 


Expected Result: Storage class conversion plans shouldn’t have migstorage reference. 

Additional Info:

$ oc get migplan test -n openshift-migration -o yaml

apiVersion: migration.openshift.io/v1alpha1
kind: MigPlan
metadata:
  annotations:
    migration.openshift.io/selected-migplan-type: scc
  name: test
  namespace: openshift-migration
  resourceVersion: "130686"
  uid: 5619f576-3572-4801-9217-f145ca68a6f3
spec:
  destMigClusterRef:
    name: host
    namespace: openshift-migration
  migStorageRef:
    name: automatic
    namespace: openshift-migration
  namespaces:
  - quay-enterprise
  persistentVolumes:
  - capacity: 5Gi
    name: pvc-76d9ad46-7d73-4a3e-a77d-29175d498a90
    proposedCapacity: 5Gi
    pvc:
      accessModes:
      - ReadWriteOnce
      hasReference: true
      name: postgres-storage:postgres-storage-new
      namespace: quay-enterprise
    selection:
      action: copy
      copyMethod: filesystem
      storageClass: standard
    storageClass: standard
    supported:
      actions:
      - skip
      - copy
      copyMethods:
      - filesystem
      - snapshot
  - capacity: 10Gi
    name: pvc-fea1a215-ad62-4df7-852f-dab11975d84a
    proposedCapacity: 10Gi
    pvc:
      accessModes:
      - ReadWriteOnce
      hasReference: true
      name: quay-storage:quay-storage-new
      namespace: quay-enterprise
    selection:
      action: copy
      copyMethod: filesystem
      storageClass: standard
    storageClass: standard
    supported:
      actions:
      - skip
      - copy
      copyMethods:
      - filesystem
      - snapshot
  srcMigClusterRef:
    name: host
    namespace: openshift-migration
status:
  conditions:
  - category: Advisory
    lastTransitionTime: "2022-04-25T07:54:19Z"
    message: This is an intra-cluster migration plan and none of the source namespaces are mapped to different destination namespaces. This plan can only be used for Storage Conversion.
    reason: StorageConversionPlan
    status: "True"
    type: MigrationTypeIdentified
  - category: Required
    lastTransitionTime: "2022-04-25T07:54:42Z"
    message: The `persistentVolumes` list has been updated with discovered PVs.
    reason: Done
    status: "True"
    type: PvsDiscovered
  - category: Required
    lastTransitionTime: "2022-04-25T07:54:42Z"
    message: The storage resources have been created.
    reason: Done
    status: "True"
    type: StorageEnsured
  - category: Required
    lastTransitionTime: "2022-04-25T07:54:42Z"
    message: The migration plan is ready.
    status: "True"
    type: Ready
  destStorageClasses:
  - accessModes:
    - ReadWriteOnce
    - ReadOnlyMany
    default: true
    name: standard
    provisioner: kubernetes.io/gce-pd
  - accessModes:
    - ReadWriteOnce
    name: standard-csi
    provisioner: pd.csi.storage.gke.io
  excludedResources:
  - imagetags
  - templateinstances
  - clusterserviceversions
  - packagemanifests
  - subscriptions
  - servicebrokers
  - servicebindings
  - serviceclasses
  - serviceinstances
  - serviceplans
  - operatorgroups
  - events
  - events.events.k8s.io
  - rolebindings.authorization.openshift.io
  observedDigest: b82617a75da2acea85ca258df37a826ab735cbbc3e4d66f6518dfa17d440f4bc
  srcStorageClasses:
  - accessModes:
    - ReadWriteOnce
    - ReadOnlyMany
    default: true
    name: standard
    provisioner: kubernetes.io/gce-pd
  - accessModes:
    - ReadWriteOnce
    name: standard-csi
    provisioner: pd.csi.storage.gke.io