gpodder.model: Remove the "set progress to 1 if it's downloaded" logic

This doesn't work for the visual representation

src/gpodder/model.py

@@ -242,9 +242,7 @@ def download(self, progress_callback):
 
     def download_progress(self):
         task = self.download_task
-        if self.state == gpodder.STATE_DOWNLOADED:
-            return 1.0
-        elif task is None:
+        if task is None:
             return 0.0
         elif not self.downloading:
             return 0.0