Bug 1749301 - Do not clear app lifetime metrics if sending deletion-request ping on init

[brizental]

This is how deletion-request pings were looking like before the fix.

 (Glean.core.Pings.Maker) {
  "ping_info": {
    "seq": 0,
    "start_time": "2022-01-10T14:36+01:00",
    "end_time": "2022-01-10T14:36+01:00"
  },
  "client_info": {
    "telemetry_sdk_build": "0.29.0",
    "client_id": "da8d1774-2704-4828-ac4c-e2949f55d887",
    "first_run_date": "2022-01-10+01:00"
  }
}

Pull Request checklist

• Quality: Make sure this PR builds and runs cleanly.
  • Inside the glean/ folder, run:
    • npm run test Runs all tests
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• Tests: This PR includes thorough tests or an explanation of why it does not
• Changelog: This PR includes a changelog entry to CHANGELOG.md or an explanation of why it does not need one
• Documentation: This PR includes documentation changes, an explanation of why it does not need that or a follow-up bug has been filed to do that work

[badboy]

That's a nasty one. kudos for finding and fixing that.