[arte] Rework extractors

* Reimplement embed and playlist extractors to delegate to the single entrypoint artetv extractor
  Beware reluctant download archive extractor keys breakage.
* Improve embeds detection (closes #27057)
- Remove obsolete code

youtube_dl/extractor/extractors.py

@@ -58,7 +58,7 @@ from .ard import (
     ARDMediathekIE,
 )
 from .arte import (
-    ArteTVPlus7IE,
+    ArteTVIE,
     ArteTVEmbedIE,
     ArteTVPlaylistIE,
 )