Change description message on internal migration

First step to address #258

src/services/migration/HomePharsXmlMigration.php

@@ -16,14 +16,11 @@ public function mustMigrate(): bool {
     }
 
     public function getDescription(): string {
-        return 'Change the name of the list of all installed Phars file.';
+        return 'Rename internal storage file from `phars.xml` to `registry.xml`.';
     }
 
     protected function doMigrate(Filename $legacy, Filename $new): void {
         $new->putContent($legacy->read()->getContent());
     }
 
-    protected function getFileDescription(): string {
-        return 'list of installed phars';
-    }
 }