[math-input] Remove unneeded yarn.lock in math-input (#167)
[math-input] Remove unneeded yarn.lock in math-input (#167)

## Summary:

Removes the local `yarn.lock` file in the math-input dir. The yarn workspace manages a single one at the repo root.

Issue: LP-11432

## Test plan:

Author: jeremywiebe

Reviewers: kevinbarabash

Required Reviewers:

Approved By: kevinbarabash

Checks: ❌ Lint, flow, and coverage check (ubuntu-latest, 16.x), ⌛ Extract i18n strings (ubuntu-latest, 16.x), ❌ Test (ubuntu-latest, 16.x), ❌ Lint, flow, and coverage check (ubuntu-latest, 16.x), ❌ Test (ubuntu-latest, 16.x), ✅ Extract i18n strings (ubuntu-latest, 16.x)

Pull Request URL: https://github.com/Khan/perseus/pull/167
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