Remove unknwon files that are in the downloads dir

The files are supposed to be downloaded in a privileged location
that the user can't access. If the user wipes the data of the
application, the updates downloaded are not removed. Perform a
one-time cleanup so that our downloads dir doesn't grow without
control.

src/org/lineageos/updater/controller/UpdaterController.java

@@ -79,6 +79,8 @@ public class UpdaterController implements UpdaterControllerInt {
         mWakeLock = powerManager.newWakeLock(PowerManager.PARTIAL_WAKE_LOCK, "Updater");
         mWakeLock.setReferenceCounted(false);
 
+        Utils.cleanupDownloadsDir(context);
+
         for (UpdateDownload update : mUpdatesDbHelper.getUpdates()) {
             addUpdate(update, false);
         }