Update to user override deleteion to preserve system overrides

Previously override deletion would delete the entire helm
override entry, now it only deletes the user_overrides dict

Change-Id: If4b23ebd1a705e678e779491b85c72e95d9fccb6
Story: 2003909
Task: 27647
Signed-off-by: Tyler Smith <tyler.smith@windriver.com>

sysinv/sysinv/sysinv/sysinv/api/controllers/v1/helm_charts.py

@@ -212,6 +212,7 @@ class HelmChartsController(rest.RestController):
         """
         self.validate_name_and_namespace(name, namespace)
         try:
-            pecan.request.dbapi.helm_override_destroy(name, namespace)
+            pecan.request.dbapi.helm_override_update(name, namespace,
+                                                     {'user_overrides': None})
         except exception.HelmOverrideNotFound:
             pass