chore: Comment out backstory in generation_config.yaml (#13351)

backstory is a top level, non-versioned proto only module. This caused
the [library
generation](https://github.com/googleapis/google-cloud-java/actions/runs/26861145003)
to fail.
Considering that Librarian is taking over, we are not going to fix the
hermetic build scripts. Commenting out the section so the daily
generation can still continue and we can compare the daily hermetic
build generation with the Librarian generation.

Author: blakeli0

generation_config.yaml

@@ -284,21 +284,21 @@ libraries:
   GAPICs:
   - proto_path: google/cloud/automl/v1
   - proto_path: google/cloud/automl/v1beta1
-- api_shortname: backstory
-  name_pretty: Malachite Common Protos
-  product_documentation: https://cloud.google.com/chronicle/docs/secops/secops-overview
-  api_description: Common Universal Data Model (UDM) and Entity protos used by Chronicle.
-  client_documentation: 
-    https://cloud.google.com/java/docs/reference/google-cloud-backstory/latest/overview
-  release_level: preview
-  distribution_name: com.google.cloud:google-cloud-backstory
-  api_id: backstory.googleapis.com
-  library_type: GAPIC_AUTO
-  group_id: com.google.cloud
-  cloud_api: true
-  GAPICs:
-  - proto_path: backstory
-  requires_billing: true
+# - api_shortname: backstory
+#   name_pretty: Malachite Common Protos
+#   product_documentation: https://cloud.google.com/chronicle/docs/secops/secops-overview
+#   api_description: Common Universal Data Model (UDM) and Entity protos used by Chronicle.
+#   client_documentation: 
+#     https://cloud.google.com/java/docs/reference/google-cloud-backstory/latest/overview
+#   release_level: preview
+#   distribution_name: com.google.cloud:google-cloud-backstory
+#   api_id: backstory.googleapis.com
+#   library_type: GAPIC_AUTO
+#   group_id: com.google.cloud
+#   cloud_api: true
+#   GAPICs:
+#   - proto_path: backstory
+#   requires_billing: true
 - api_shortname: backupdr
   name_pretty: Backup and DR Service API
   product_documentation: https://cloud.google.com/backup-disaster-recovery/docs/concepts/backup-dr