Fix: Replace deprecated and removed \OC_Helper with \OCP\Util

[madrzejewski]

Fix groupquota in NextCloud 32 by replacing the deprecated (and now removed) \OC_Helper with the equivalent \OCP\Util as per the documentation recommands.

[github-actions]

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[0ranki]

There's also a usages of OC_Helper::computerFileSize in
lib/Command/SetQuota.php
lib/Controller/QuotaController.php

If there's any way to be helpful for testing or otherwise, please let me know.