DOC Remove DataExtension and others

en/08_Changelogs/6.0.0.md

@@ -293,6 +293,7 @@ Injector::inst()->load([
 - [`DataObject::write()`](api:SilverStripe\ORM\DataObject::write()) has a new boolean `$skipValidation` parameter. This can be useful for scenarios where you want to automatically create a new record with no data initially without restricting how developers can set up their validation rules.
 - [`FieldList`](api:SilverStripe\Forms\FieldList) is now strongly typed. Methods that previously allowed any iterable variables to be passed, namely [`FieldList::addFieldsToTab()`](api:SilverStripe\Forms\FieldList::addFieldsToTab()) and [`FieldList::removeFieldsFromTab()`](api:SilverStripe\Forms\FieldList::removeFieldsFromTab()), now require an array to be passed instead.
 - [`BaseElement::getDescription()`](api:DNADesign\Elemental\Models\BaseElement::getDescription()) has been removed. If you had implemented this method in your custom elemental blocks, either set the [`description`](api:DNADesign\Elemental\Models\BaseElement->description) configuration property or override the [`getTypeNice()`](api:DNADesign\Elemental\Models\BaseElement::getTypeNice()) method.
+- [`DataExtension`](api:SilverStripe\ORM\DataExtension), [`SiteTreeExtension`](api:SilverStripe\CMS\Model\SiteTreeExtension), and [`LeftAndMainExtension`](api:SilverStripe\Admin\LeftAndMainExtension) have been removed. If you subclass any of these classes, you must now subclass [`Extension`](api:SilverStripe\ORM\Extension) instead.
 
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