Re-enable event stats again.

[rkooo567]

Why are these changes needed?

I tried reproducing the many pg mini integration failure from this PR; #21216, but I failed to do that. (this was the only test that became flaky when we turned on the flag last time).

I tried

• Run tests:test_placement_group_mini_integration 5 times instead of 3 (the default)
• Re-run the PR 3 times.

So I think it is worth trying re-enabling it again.

Related issue number

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• I've run scripts/format.sh to lint the changes in this PR.
• I've included any doc changes needed for https://docs.ray.io/en/master/.
• I've made sure the tests are passing. Note that there might be a few flaky tests, see the recent failures at https://flakey-tests.ray.io/
• Testing Strategy
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  • This PR is not tested :(