Remove JavaScript decorators package

[aduth]

🛠 Summary of changes

Removes the @18f/identity-decorators JavaScript package and updates the single remaining usage to remove the memoization usage.

Why?

• While the once decorator was meant to be used as a memoization technique, it may have been a premature optimization for our current usage.
• The TC39 decorator proposal is not final, and our implementation targeted a now-deprecated version of the proposed specification, and would eventually require a rewrite.
• Because decorators are currently non-standard to the language, it could create onboarding barriers for new developers.
• Reduces compiled bundle size, number of dependencies, and complexity of the build pipeline.

📜 Testing Plan

• yarn test