appveyor: Remove Meson job.

Appveyor Meson fails misteriously some times, e.g.,
- https://ci.appveyor.com/project/mesa3d/mesa/builds/31780753/job/w8b28iahboxq4na2
- https://ci.appveyor.com/project/mesa3d/mesa/builds/31857376
and now that we have msvc coverage on gitlab ci this is no longer necessary.

Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4392>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4392>

appveyor.yml

@@ -53,9 +53,6 @@ environment:
   matrix:
   - compiler: msvc
     buildsystem: scons
-  - compiler: msvc
-    buildsystem: meson
-    path: C:\Python38-x64;C:\Python38-x64\Scripts;%path%
 
 install:
 - cmd: .appveyor\appveyor_msvc.bat install