Update q2a v1.7:
Go to /admin/viewing and disable "Show edits/updates in post meta:"
In qa-includes/qa-app-format.php I found the lines for that starting from comment "Updated when and by whom".
There is a toggle: @$options['updateview'] which I found defined in qa-app-options.php line 536: 'updateview' => true,
I changed it to 'updateview' => false,
and it seems to work.
No edit-/tag-updates visibile anymore!