test: Remove old, outdated kubectl cp command

Author: Techassi

tests/templates/kuttl/upgrade/04-prepare-test-nifi.yaml.j2

@@ -2,7 +2,6 @@
 apiVersion: kuttl.dev/v1beta1
 kind: TestStep
 commands:
-  - script: kubectl cp -n $NAMESPACE ./test_nifi_metrics.py  test-nifi-0:/tmp
   - script: kubectl cp -n $NAMESPACE ./test_nifi.py  test-nifi-0:/tmp
   - script: kubectl cp -n $NAMESPACE ./flow.py  test-nifi-0:/tmp
   - script: kubectl cp -n $NAMESPACE ./generate-and-log-flowfiles.json test-nifi-0:/tmp