Remove deprecated ember-flight-icon lazyEmbed flag

[zamoore]

📌 Summary

If merged, this PR will remove support for the deprecated lazyEmbed flag for ember-flight-icons in favor of supporting the flightIconsSpriteLazyEmbed config only.

🔗 External links

Jira ticket: HDS-4883

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👀 Component checklist

• Percy was checked for any visual regression
• A changelog entry was added via Changesets if needed (see templates here)

💬 Please consider using conventional comments when reviewing this PR.

📋 PCI review checklist

• If applicable, I've documented a plan to revert these changes if they require more than reverting the pull request.
• If applicable, I've worked with GRC to document the impact of any changes to security controls.
  Examples of changes to controls include access controls, encryption, logging, etc.
• If applicable, I've worked with GRC to ensure compliance due to a significant change to the in-scope PCI environment.
  Examples include changes to operating systems, ports, protocols, services, cryptography-related components, PII processing code, etc.

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[alex-ju]

When removing deprecated features, I think we should consider the following:

• How many consumers are still using this feature? (to gauge the impact)
• What upgrade path exists for consumers relying on emberFlightIcons.lazyEmbed? (to ensure a solution is available)
• How will consumers know how to address this breaking change? (to provide clear documentation)

The answers to these questions should guide the 'how to migrate' instructions in the changelog.