v-m/alerts: Remove 'no file changes' alert

It turns out this alert is not very useful, and indeed quite annoying.
Many servers can go for days or even weeks with no changes, which is
completely normal.

victoria-metrics/alerts.yml

@@ -232,25 +232,6 @@ groups:
         Clients are scheduled to back up every day, but at least one has not
         been backed up in at least 7 days.  Check the Restic configuration on
         that system to ensure backups are running properly.
-  - alert: No File Changes
-    expr: >-
-      max_over_time(
-        abs(
-          delta(
-            sum(restic_backup_size_total{
-              client_hostname!="pxe0.pyrocufflink.blue",
-              client_hostname!="web0.pyrocufflink.blue",
-            })
-              by (client_hostname, client_username)
-          )
-        )[7d]
-      ) == 0
-    annotations:
-      summary: The size of the Restic backup has not changed
-      description: >-
-        The size of the Restic backup for a particular client has not changed
-        in at least 7 days.  This may indicate that the backup configuration
-        is incorrect.
 
 - name: Paperless-ngx
   rules: