numberFormat should support blank "thousandsSep"

[beaucollins]

Steps to reproduce

cd path/to/wp-calypso`
npm run build
node

const { numberFormat } = require('./packages/i18n-calypso/cjs/');
numberFormat(9999, { thousandsSep: '', });

What I expected

Output of 9999.

What happened instead

Output of 9,999.

Browser / OS version

None/Mac OS 10.15.3

Screenshot / Video

[stale]

This issue has been marked as stale and will be closed in seven days. This happened because:

• It has been inactive in the past 9 months.
• It isn't a project or a milestone, and hasn’t been labeled `[Pri] Blocker`, `[Pri] High`, `[Status] Keep Open`, or `OSS Citizen`.

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