Remove unused comments from _initDiscount() function

[mageprince]

Description

Remove unused comments from _initDiscount() function of Tax.php

Fixed Issues (if relevant)

N/A

Manual testing scenarios

N/A

Contribution checklist

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)

[magento-engcom-team]

Hi @mageprince. Thank you for your contribution
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[VladimirZaets]

Hi @mageprince. Thanks for the collaboration. Remove commented code is ok, but
due to Magento backward-compatible guide we can't change method signature. The method should, as previously returns void.

[mageprince]

@VladimirZaets Thanks for the review. I have updated method signature.

[magento-engcom-team]

Hi @mageprince. Thank you for your contribution.
We will aim to release these changes as part of 2.3.0.
Please check the release notes for final confirmation.