Clear cache when GDPR Erasure Request tool is run

[raamdev]

The GDPR Erasure Request tool which can anonymize the comments of a user needs to trigger an automatic clearing of the cache, so that when the erasure tool is used the site does not continue to show the cached comments.

Comet Cache should hook into ``wp_privacy_personal_data_erased` to trigger a Clear Cache when that action is fired. https://developer.wordpress.org/plugins/privacy/privacy-related-options-hooks-and-capabilities/

[garretthyder]

Thanks for making this a priority @raamdev