[extractor/vrt] Overhaul extractors (#6244)

* Fixes `VrtNU` extractor to work with the VRT MAX site change
* Adapts `VRT`, `Ketnet` and `DagelijkseKost` extractors to the new VRT API
* Removes `Canvas` and `CanvasEen` extractors; the sites and API no longer exist
* Moves all remaining VRT-related extractors into the `vrt` module

Closes #4908
Authored by: jeroenj, bergoid, bashonly

Co-authored-by: bergoid <bergoid@users.noreply.github.com>
Co-authored-by: bashonly <88596187+bashonly@users.noreply.github.com>

yt_dlp/extractor/_extractors.py

@@ -295,12 +295,6 @@ from .camwithher import CamWithHerIE
 from .canalalpha import CanalAlphaIE
 from .canalplus import CanalplusIE
 from .canalc2 import Canalc2IE
-from .canvas import (
-    CanvasIE,
-    CanvasEenIE,
-    VrtNUIE,
-    DagelijkseKostIE,
-)
 from .carambatv import (
     CarambaTVIE,
     CarambaTVPageIE,
@@ -894,7 +888,6 @@ from .karaoketv import KaraoketvIE
 from .karrierevideos import KarriereVideosIE
 from .keezmovies import KeezMoviesIE
 from .kelbyone import KelbyOneIE
-from .ketnet import KetnetIE
 from .khanacademy import (
     KhanAcademyIE,
     KhanAcademyUnitIE,
@@ -2285,7 +2278,12 @@ from .voxmedia import (
     VoxMediaVolumeIE,
     VoxMediaIE,
 )
-from .vrt import VRTIE
+from .vrt import (
+    VRTIE,
+    VrtNUIE,
+    KetnetIE,
+    DagelijkseKostIE,
+)
 from .vrak import VrakIE
 from .vrv import (
     VRVIE,