Remove dead-code branch for DASH formats

These are not provided by the site. Plus, without an example to test
against, it is unclear how these formats need to be treated to be sorted
correctly.

yt_dlp/extractor/zdf.py

@@ -118,10 +118,7 @@ class ZDFBaseIE(InfoExtractor):
                         if ext == 'm3u8':
                             fmts = self._extract_m3u8_formats(
                                 format_url, video_id, 'mp4', m3u8_id='hls', fatal=False)
-                        elif ext == 'mpd':
-                            fmts = self._extract_mpd_formats(
-                                format_url, video_id, mpd_id='dash', fatal=False)
-                        else:
+                        elif ext in ('mp4', 'webm'):
                             height = int_or_none(quality.get('highestVerticalResolution'))
                             width = round(aspect_ratio * height) if aspect_ratio and height else None
                             fmts = [{
@@ -132,6 +129,10 @@ class ZDFBaseIE(InfoExtractor):
                                 'format_id': join_nonempty('http', stream.get('type')),
                                 'tbr': int_or_none(self._search_regex(r'_(\d+)k_', format_url, 'tbr', default=None)),
                             }]
+                        else:
+                            self.write_debug(f'Unsupported extension {ext} ({format_url}).')
+                            fmts = []
+
                         f_class = variant.get('class')
                         for f in fmts:
                             formats.append({