Fix flaky TestDeleteSnapshots by using fixed point in time
Created by: mrnugget
As reported by @valerybugakov on Slack, the test seems to fail when the current time is >24hrs off from the time stored in the autogold fixture file.
So what I did here is to use a fixed point in time (since time.Now
didn't seem relevant to the tests) and save that in the autogold file. I
also updated the other tests to use this point in time.