Remove write to the unused and undeclared property

This solves the deprecation warning about using dynamic properties.
Turns out the code wasn't written in legacy way but the property
was just never meant to be written as it's unused.

scripts/translation/lib/RevcheckRun.php

@@ -123,7 +123,6 @@ private function calculateStatus()
 
             // TranslatedOld
 
-            $source->days = $daysOld;
             $source->status = RevcheckStatus::TranslatedOld;
             $this->filesOld[] = $source;
         }