office-js: Clean up taskpane

[ElizabethSamuel-MSFT]

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[typescript-bot]

@ElizabethSamuel-MSFT Thank you for submitting this PR!

🔔 @OfficeDev @LanceEa @Zlatkovsky @kbrandl @Rick-Kirkham @AlexJerabek - please review this PR in the next few days. Be sure to explicitly select Approve or Request Changes in the GitHub UI so I know what's going on.

If no reviewer appears after a week, a DefinitelyTyped maintainer will review the PR instead.

[typescript-bot]

A definition owner has approved this PR ⭐️. A maintainer will merge this PR shortly. If it shouldn't be merged yet, please leave a comment saying so and we'll wait. Thank you for your contribution to DefinitelyTyped!