[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/megaphone.py

@@ -1,5 +1,3 @@
-import re
-
 from .common import InfoExtractor
 from ..utils import js_to_json
 
@@ -8,6 +6,7 @@ class MegaphoneIE(InfoExtractor):
     IE_NAME = 'megaphone.fm'
     IE_DESC = 'megaphone.fm embedded players'
     _VALID_URL = r'https://player\.megaphone\.fm/(?P<id>[A-Z0-9]+)'
+    _EMBED_REGEX = [rf'<iframe[^>]*?\ssrc=["\'](?P<url>{_VALID_URL})']
     _TEST = {
         'url': 'https://player.megaphone.fm/GLT9749789991?"',
         'md5': '4816a0de523eb3e972dc0dda2c191f96',
@@ -45,8 +44,3 @@ class MegaphoneIE(InfoExtractor):
             'duration': episode_data['duration'],
             'formats': formats,
         }
-
-    @classmethod
-    def _extract_urls(cls, webpage):
-        return [m[0] for m in re.findall(
-            r'<iframe[^>]*?\ssrc=["\'](%s)' % cls._VALID_URL, webpage)]