Support feedparser 6, based on https://github.com/quodlibet/quodlibet/pull/3464

--- a/quodlibet/browsers/audiofeeds.py
+++ b/quodlibet/browsers/audiofeeds.py
@@ -137,7 +137,4 @@ class Feed(list):
     def parse(self):
         try:
-            if not self._check_feed():
-                return False
-
             doc = feedparser.parse(self.uri)
         except Exception as e: