Remove wrapper for metrics in the "metrics" category

[mcarare]

Breakout from #21292.

Note: The category is a legacy "mistake" but creating separate elements is not the scope of this ticket, as it would break existing dashboards.

┆Issue is synchronized with this Jira Task

[sflorean]

Verified as fixed on Nightly 4/18 with OnePlus 9 (Android 12).

{
          "timestamp": 10571,
          "category": "events",
          "name": "performed_search",
          "extra": {
            "source": "default.suggestion"
          }
        },
        {
          "timestamp": 10572,
          "category": "awesomebar",
          "name": "search_suggestion_clicked"
        },
{
          "timestamp": 15491,
          "category": "awesomebar",
          "name": "history_suggestion_clicked"
        },
 {
          "timestamp": 19388,
          "category": "search_shortcuts",
          "name": "selected",
          "extra": {
            "engine": "DuckDuckGo"
          }
        {
          "timestamp": 20954,
          "category": "events",
          "name": "performed_search",
          "extra": {
            "source": "shortcut.action"
          }