Fix Event Grid SQLSTATE error.

[sebastic]

As reported in #4852, the Event Grid is broken in 2.11.0 because the timestamp column is converted from bigint to timestamp, but it already is. The from_unixtime function call is no longer required.

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[sebastic]

I don't have time to review CLA terms, you can use my changes in this PR as you see fit, I disclaim any copyright.