Retrieve approle_secret_id from correct relation

The existing comment in the code expresses the correct intent:
"fetch current secret-id, if any, from relation with barbican principle"
but then attempts to retrieve the secret-id from the vault
relation.

Change-Id: Ie2694ba38e08fd9e864bf9d8fa0b63f0e185b8bd
Closes-Bug: #1871981

src/reactive/barbican_vault_handlers.py

@@ -77,9 +77,8 @@ def plugin_info_barbican_publish():
 
     # fetch current secret-id, if any, from relation with barbican principle
     current_secret_id = None
-    secrets = reactive.endpoint_from_flag('secrets.available')
-    if secrets:
-        for relation in secrets.relations:
+    if barbican:
+        for relation in barbican.relations:
             data = relation.to_publish.get('data')
             if data and data.get('approle_secret_id'):
                 current_secret_id = data.get('approle_secret_id')

unit_tests/test_barbican_vault_handlers.py

@@ -119,8 +119,7 @@ class TestBarbicanVaultHandlers(test_utils.PatchHelper):
         handlers.plugin_info_barbican_publish()
         self.endpoint_from_flag.assert_has_calls([
             mock.call('endpoint.secrets.joined'),
-            mock.call('secrets-storage.available'),
-            mock.call('secrets.available'),
+            mock.call('secrets-storage.available')
         ])
         vault_data = {
             'approle_role_id': secrets_storage.unit_role_id,