fix(sql-exporter): Remove tenant_id from compute_logical_snapshot_files

It appeared to be that it's already auto-added to all metrics [1]

[1]: https://github.com/neondatabase/flux-fleet/blob/3a907c317c1e4515190b04a8726e00a9f976214a/apps/base/ext-vmagent/vmagent.yaml#L43

Author: ololobus

vm-image-spec.yaml

@@ -329,12 +329,10 @@ files:
         type: gauge
         help: 'Number of snapshot files in pg_logical/snapshot'
         key_labels:
-          - tenant_id
           - timeline_id
         values: [num_logical_snapshot_files]
         query: |
           SELECT
-            (SELECT setting FROM pg_settings WHERE name = 'neon.tenant_id') AS tenant_id,
             (SELECT setting FROM pg_settings WHERE name = 'neon.timeline_id') AS timeline_id,
             -- Postgres creates temporary snapshot files of the form %X-%X.snap.%d.tmp. These
             -- temporary snapshot files are renamed to the actual snapshot files after they are