Tests: remove all files not in repository.

Author: xoviat

appveyor.yml

@@ -122,10 +122,7 @@ on_finish:
       )
       $LastExitCode = 0
   
-  - ps: |
-      cd build
-      ls -filter *.py -recurse | foreach {rm $_.fullname}
-      cd ..
+  - git clean -dfx --exclude=sonar
 
   - ps: |
       if (-Not $env:APPVEYOR_PULL_REQUEST_NUMBER) {