chore(utils): resolve jsdoc lint suppressions

[cryptodev-2s]

Explanation

Clears the 3 jsdoc suppressions the @metamask/utils migration left in eslint-suppressions.json.

mnemonic.ts and promise.ts were missing a blank line between the block description and the first tag. forceRemove in fs.ts returned the result of fs.promises.rm, which made jsdoc/require-returns ask for a @returns on a function declared Promise<void>. Dropped the redundant return instead, matching ensureDirectoryStructureExists right above it.

No API or behaviour change, so no changelog entry.

References

Follows #10185

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 communicated my changes to consumers by updating changelogs for packages I've changed
• I've introduced breaking changes in this PR and have prepared draft pull requests for clients and consumer packages to resolve them