Don't warn about Artifact Store 404s
Don't warn about Artifact Store 404s

Summary:
An incredible majority of our Sentry alerts are 404s from AS, but they don't signal a problem
necessarily and they may be masking other issues.
Better to ignore the 404s for now until we have a reasonable way to know when they're a problem.

Test Plan: None

Reviewers: anupc

Reviewed By: anupc

Subscribers: changesbot

Differential Revision: https://tails.corp.dropbox.com/D150829

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