Update Metrics CollecTor check to remove Torperf files
We stopped archiving Torperf files in #34141 (moved), and now the check starts complaining about them not being recent anymore: CRITICAL: Got a valid response from https://collector.torproject.org/index/index.json with at least one timestamp being critically outdated: /recent/torperf/ = 2020-05-16 00:10 (33 = 30 + 3 hours ago)
I'm attaching a patch.
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