Feature remove File extension for backlink tracking in favour of UsedOnTable form field

_config/asset-admin.yml

@@ -1,8 +0,0 @@
----
-Name: cms-asset-admin
-OnlyIf:
-  ModuleExists: silverstripe/asset-admin
----
-SilverStripe\AssetAdmin\Forms\FileFormFactory:
-  extensions:
-    - SilverStripe\CMS\Model\SiteTreeFileFormFactoryExtension

code/Model/SiteTreeFileFormFactoryExtension.php

@@ -3,14 +3,18 @@
 namespace SilverStripe\CMS\Model;
 
 use SilverStripe\Assets\File;
+use SilverStripe\Dev\Deprecation;
 use SilverStripe\Forms\FieldList;
-use SilverStripe\Forms\ReadonlyField;
 use SilverStripe\Forms\Tab;
 use SilverStripe\Forms\TabSet;
 use SilverStripe\ORM\DataExtension;
-use SilverStripe\ORM\FieldType\DBHTMLText;
+use SilverStripe\Admin\Forms\UsedOnTable;
+use SilverStripe\Versioned\RecursivePublishable;
 
 /**
+ * @deprecated 5.0
+ * No longer required - superceded by {@see UsedOnTable}
+ *
  * Extension applied to {@see FileFormFactory} to decorate with a "Used on:" information area.
  * Uses tracking provided by {@see SiteTreeFileExtension} to generate this.
  *
@@ -20,30 +24,22 @@ class SiteTreeFileFormFactoryExtension extends DataExtension
 {
     public function updateFormFields(FieldList $fields, $controller, $formName, $context)
     {
-        // Create field
-        /** @var File|SiteTreeFileExtension $record */
-        $record = $context['Record'];
-        $usedOnField = ReadonlyField::create(
-            'BackLinkCount',
-            _t(__CLASS__.'.BACKLINKCOUNT', 'Used on:'),
-            $record->BackLinkTrackingCount() . ' ' . _t(__CLASS__.'.PAGES', 'page(s)')
-        )
-            ->addExtraClass('cms-description-toggle');
-
-        // Add table
-        /** @var DBHTMLText $backlinkHTML */
-        $backlinkHTML = $record->BackLinkHTMLList();
-        if (trim($backlinkHTML->forTemplate())) {
-            $usedOnField->setDescription($backlinkHTML);
-        }
-
         /** @var TabSet $tabset */
         $tabset = $fields->fieldByName('Editor');
-        if ($tabset) {
+        if (!$tabset) {
+            return;
+        }
+        $class = UsedOnTable::class;
+        Deprecation::notice('5.0', "Use the $class to show this table");
+
+        /** @var File|SiteTreeFileExtension|RecursivePublishable $record */
+        $record = $context['Record'];
+
+        $usedOnField = UsedOnTable::create('UsedOnTableReplacement', $record);
+
         // Add field to new tab
         /** @var Tab $tab */
         $tab = Tab::create('Usage', _t(__CLASS__ . '.USAGE', 'Usage'), $usedOnField);
         $tabset->push($tab);
     }
 }
-}