[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/bpb.py

@@ -47,7 +47,7 @@ class BpbIE(InfoExtractor):
             quality = 'high' if '_high' in video_url else 'low'
             formats.append({
                 'url': video_url,
-                'preference': 10 if quality == 'high' else 0,
+                'quality': 10 if quality == 'high' else 0,
                 'format_note': quality,
                 'format_id': '%s-%s' % (quality, determine_ext(video_url)),
             })