Remove check for `authPublicKey` when claiming jobs

[calumcalder]

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This check was originally added in 9d5302c, where it was used to check that two workers didn't attempt to claim the same job. Since then the surrounding code has seen a lot of refactoring, including migrating to calling claimJob on the job store which, per the comment in JobPollingService and on the JobStore interface docs, should do the job of ensuring this doesn't happen.

Removing this line unblocks the option of allowing workers to reclaim jobs from another crashed worker that couldn't inform the job store it was exiting (e.g. OOM killed), but also continues to allow blocking claimJob on claimed jobs by delegating that decision to the JobStore.

[CLAassistant]

All committers have signed the CLA.

[calumcalder]

Thanks for the review! Just waiting on legal to review the new CLA after the switch to DTI ownership

[calumcalder]

CLA signed 👍