Clear comment transients only on wp_update_comment_count

Does not need to be flushed when editing a product. Part of #5777
No need to clear all transients here - only clear parent's cache

Part of #5777
Remove wp_cache_flush() Closes #5777

Carrying on from previous commits, the need for a wildcard delete for
products is unnecessary. This removes the $wpdb query and
wp_cache_flush()
Invalidate query transients to avoid cache flush

Part of #5777. These transients are required and cannot be predicted.

If not using an external cache system, the DB is cleared still to keep
size down after invalidation.

For these 2 transients, invalidation occurs when visibility altering
product attributes are edited.