[extractors] Use new framework for existing embeds (#4307)

`Brightcove` is difficult to migrate because it's subclasses may depend
on the signature of the current functions. So it is left as-is for now

Note: Tests have not been migrated

yt_dlp/extractor/sendtonews.py

@@ -43,14 +43,14 @@ class SendtoNewsIE(InfoExtractor):
     _URL_TEMPLATE = '//embed.sendtonews.com/player2/embedplayer.php?SC=%s'
 
     @classmethod
-    def _extract_url(cls, webpage):
+    def _extract_embed_urls(cls, url, webpage):
         mobj = re.search(r'''(?x)<script[^>]+src=([\'"])
             (?:https?:)?//embed\.sendtonews\.com/player/responsiveembed\.php\?
                 .*\bSC=(?P<SC>[0-9a-zA-Z-]+).*
             \1>''', webpage)
         if mobj:
             sc = mobj.group('SC')
-            return cls._URL_TEMPLATE % sc
+            yield cls._URL_TEMPLATE % sc
 
     def _real_extract(self, url):
         playlist_id = self._match_id(url)