Delete Appveyor config (ref #5410)

.appveyor.yml

@@ -1,15 +0,0 @@
-version: '{build}'
-branches:
-  only: [master]
-init:
-- ps: Install-Product node 8
-install:
-- cmd: npm -v 
-- cmd: node -v 
-- cmd: npm install -g yarn
-- cmd: yarn
-cache:
-- node_modules
-build: off
-test_script:
-- cmd: yarn test