deletes don't affect stale metrics. They may resurface if max-stale gets increased

[Dieterbe]

Consider:
A metric that is stale and thus doesn't live in MT's memory index but still lives in the regular table if it haven't been archived yet).
A delete query won't catch it. Normally this is fine. the metric won't be in the memory index and thus it can't be queried for data. If new data comes in, it will become un-stale and resurface its data. But that's the same behavior as the normal delete case of non-stale metrics, which also resurface if new data comes in.

Where this gets interesting though:

1. if you increase the max-stale time window, the metrics may resurface by themselves
2. revive functionality, as proposed in Ability to "revive" archived series #1976 may also mistakenly reintroduce metrics that may needed to be deleted. (as delete queries can't reach into the archive table)

[Dieterbe]

I think this is an acceptable limitation.

[stale]

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