chore: remove stale Skyfire-specific utilities after PaymentProvider refactor

[jirispilka]

Summary

Follow-up cleanup after the PaymentProvider refactor (#590). Several Skyfire-specific standalone functions are now superseded by methods on SkyfirePaymentProvider and should be removed.

Changes

• Remove redactSkyfirePayId from src/utils/logging.ts — superseded by SkyfirePaymentProvider.redactForLogging() on the provider interface; remove deprecated re-export from index_internals.ts
• Remove dead applySkyfireAugmentation / isSkyfireEligible from src/utils/tools.ts — superseded by SkyfirePaymentProvider.decorateToolSchema()
• Replace Skyfire-specific comments/messages with provider-agnostic wording in call_actor_common.ts, actor_execution.ts, actor_tools_factory.ts, and actor_details.ts
• Update unit tests to target SkyfirePaymentProvider.redactForLogging() and decorateToolSchema() instead of the removed standalone functions

Notes

• redactSkyfirePayId is currently still exported from index_internals.ts for backward compatibility with apify-mcp-server-internal. Coordinate removal with an update to the internal repo.
• In actor_execution.ts, the input passed to callActorGetDataset is already payment.cleanArgs (payment fields stripped by preparePayment()), so no redaction call is needed there at all.