prometheus-mixin: remove PrometheusTSDBWALCorruptions

The counter is only increased when tsdb.Open() is called which
Prometheus does only once in its lifetime (when it initializes). If the
corruption can't be recovered, tsdb.Open() returns an error and
Prometheus exits. Hence the metric is either 0 (no corruption) or 1
(corruption detected and repaired). If the latter, the alert isn't
actionable and the only way to resolve it is to restart Prometheus which
would reset the counter.

Signed-off-by: Simon Pasquier <spasquie@redhat.com>

documentation/prometheus-mixin/alerts.libsonnet

@@ -124,20 +124,6 @@
               description: 'Prometheus %(prometheusName)s has detected {{$value | humanize}} compaction failures over the last 3h.' % $._config,
             },
           },
-          {
-            alert: 'PrometheusTSDBWALCorruptions',
-            expr: |||
-              increase(tsdb_wal_corruptions_total{%(prometheusSelector)s}[3h]) > 0
-            ||| % $._config,
-            'for': '4h',
-            labels: {
-              severity: 'warning',
-            },
-            annotations: {
-              summary: 'Prometheus is detecting WAL corruptions.',
-              description: 'Prometheus %(prometheusName)s has detected {{$value | humanize}} corruptions of the write-ahead log (WAL) over the last 3h.' % $._config,
-            },
-          },
           {
             alert: 'PrometheusNotIngestingSamples',
             expr: |||