fix(3742): change getMetaMetricsId to only sync func type

[DDDDDanica]

Explanation

Changes introduced in this PR including:

• remove fallback of metaMetricsId and rely on client side always returning a value
• refactor getMetaMetricsId to only handle synchronous (extension) function

References

Addressed feedback #5051 (comment)

@metamask/remote-feature-flag-controller

• CHANGED: Modify signature of getMetaMetricsId to handle only synchronous function
• CHANGED: Remove fallback of metaMetricsId

Checklist

• I've updated the test suite for new or updated code as appropriate
• I've updated documentation (JSDoc, Markdown, etc.) for new or updated code as appropriate
• I've highlighted breaking changes using the "BREAKING" category above as appropriate
• I've prepared draft pull requests for clients and consumer packages to resolve any breaking changes

[Gudahtt]

LGTM!

Nit for the changelog in the PR description; both seem appropriate to categorize as changes, the changed getMetaMetricsId signature doesn't seem like a new feature to me.

[DDDDDanica]

@Gudahtt thanks for suggestions, modified !