[formatsort] Remove misuse of 'preference'

'preference' is to be used only when the format is better that ALL qualities of a lower preference irrespective of ANY sorting order the user requests. See deezer.py for correct use of this

In the older sorting method, `preference`, `quality` and `language_preference` were functionally almost equivalent. So these disparities doesn't really matter there

Also, despite what the documentation says, the default for `preference` was actually 0 and not -1. I have tried to correct this and also account for it when converting `preference` to `quality`

youtube_dlc/extractor/xstream.py

@@ -93,7 +93,7 @@ class XstreamIE(InfoExtractor):
             formats.append({
                 'url': link.get('href'),
                 'format_id': link.get('rel'),
-                'preference': 1,
+                'quality': 1,
             })
 
         thumbnails = [{