[factory] Retire #deduplicateQueuedGithubLifecycleAliases now that the claim key is provider-neutral

[khaliqgant]

Follow-up from #329 (#211).

#deduplicateQueuedGithubLifecycleAliases in src/orchestrator/factory.ts is a
GitHub-only compensation for the surface-path claim key. #329 replaced that key
with the work-unit identity and added a provider-neutral rekey in both state
stores, which collapses aliases before this method ever sees them.

It was deliberately left in place rather than removed in the same PR:

• it was not in the removal list the [factory] Key dispatch claims on work-unit identity, not surface path #211 ruling sequenced (that covered
  matchingGithubLifecycleEntry and the five claim.key ?? key sites);
• it still covers the one case the load-time rekey declines to touch. That pass
  has no clock, so it never judges lease expiry and leaves any work unit with
  more than one leased row untouched for the claim path to refuse precisely;
• removing a compensating mechanism in the same change that supersedes it, on
  the dispatch critical path, is how an outage happens.

What this issue should settle:

1. Whether the remaining coverage is real or whether the claim path's
   fail-closed refusal already subsumes it. Note the two disagree on policy:
   this method picks a winner among queued aliases, while the [factory] Key dispatch claims on work-unit identity, not surface path #211 ruling is
   explicit that more than one live lease must refuse rather than guess.
2. If it is redundant, remove it together with the
   dispatchLifecycleGithubAliasesCollapsed /
   dispatchLifecycleGithubAliasConflicts /
   dispatchLifecycleGithubAliasDedupeDeferred counters.

A compensating mechanism left standing after its cause is fixed becomes a
permanent source of confusion, which is why this is filed rather than left to be
noticed later.