[youtube:playlist] Correct playlist ID output

The ID now starts with PL, so we don't need to output that twice.

youtube_dl/extractor/youtube.py

@@ -1419,7 +1419,7 @@ class YoutubePlaylistIE(YoutubeBaseInfoExtractor):
                 self.to_screen(u'Downloading just video %s because of --no-playlist' % video_id)
                 return self.url_result(video_id, 'Youtube', video_id=video_id)
             else:
-                self.to_screen(u'Downloading playlist PL%s - add --no-playlist to just download video %s' % (playlist_id, video_id))
+                self.to_screen(u'Downloading playlist %s - add --no-playlist to just download video %s' % (playlist_id, video_id))
 
         if playlist_id.startswith('RD'):
             # Mixes require a custom extraction process