CI: drop app veyor in favour of GHA

.appveyor.yml

@@ -1,33 +0,0 @@
-version: '{build}'
-
-image: Ubuntu2004
-
-configuration: Release
-
-skip_branch_with_pr: true
-clone_depth: 1
-
-skip_commits:
-  files:
-    - .travis.yml
-    - .gitlab-ci.yml
-    - .azure-pipelines.yml
-    - .cirrus.yml
-
-init:
-  - ps: Update-AppveyorBuild -Version "build-$env:APPVEYOR_BUILD_NUMBER-$($env:APPVEYOR_REPO_COMMIT.substring(0,7))"
-
-install:
-  - sudo apt-get -y install libsodium-dev libcap-ng-dev
-before_build:
-  - git submodule update --init --recursive
-  - ./configure
-build_script:
-  - make package -C build -j $(nproc || sysctl -n hw.ncpu || echo 4)
-  - .ci/memory-leak-test.sh
-test_script:
-  - .ci/appveyor-deb-install-test.sh
-  - sudo apt-get update && sudo apt-get -y install autoconf libtool liblzo2-dev libpam-dev fping unzip liblz4-dev libnl-genl-3-dev # openvpn build deps
-  - sudo .ci/start-se-openvpn.sh
-  - sudo .ci/run-openvpn-tests.sh
-