appveyor: drop uploading artifacts

Uploading artifacts sometimes results in this error:
```
Uploading artifacts...
[1/1] _bld\src\curl.exe (2,022,912 bytes)...100%
Error uploading artifact to the storage: Remote server returned 503: Service Temporarily Unavailable
```
Ref: https://ci.appveyor.com/project/curlorg/curl/builds/50424126/job/e4envval6xkicv1i#L123

The artifacts are also probably not useful to upload for every run. Also
note that they were missing external DLL dependencies.

Leave the logic there commented, to make it easy to enable as needed for
debugging or testing artifacts locally.

Closes #14581

appveyor.yml

@@ -211,8 +211,8 @@ skip_commits:
     - 'packages/**/*'
     - 'plan9/**/*'
 
-artifacts:
+#artifacts:
-  - path: '**/curl.exe'
+#  - path: '**/curl.exe'
-    name: curl
+#    name: curl
-  - path: '**/*curl*.dll'
+#  - path: '**/*curl*.dll'
-    name: libcurl dll
+#    name: libcurl dll