ci(appveyor): Remove now that GHA is testing Windows

appveyor.yml

@@ -1,39 +0,0 @@
-version: '{build}'
-environment:
-  APPVEYOR_CACHE_ENTRY_ZIP_ARGS: "-t7z -m0=lzma -mx=9"
-  DEPS_BUILD_DIR: "C:/projects/nvim-deps"
-  DEPS_PREFIX: "C:/projects/nvim-deps/usr"
-  # Silence/redirect errors due to missing locking support (via libgcov).
-  GCOV_ERROR_FILE: "$(TEMP)/libgcov-errors.log"
-image: Visual Studio 2017
-configuration:
-- MINGW_64-gcov
-- MINGW_32
-- MSVC_64
-- MSVC_32
-init:
-- ps: |
-    # Pull requests: skip some build configurations to save time.
-    if ($env:APPVEYOR_PULL_REQUEST_HEAD_COMMIT -and $env:CONFIGURATION -match '^(MSVC_64|MINGW_32)$') {
-      $env:APPVEYOR_CACHE_SKIP_SAVE = "true"
-      Exit-AppVeyorBuild
-    }
-# RDP
-#- ps: iex ((new-object net.webclient).DownloadString('https://raw.githubusercontent.com/appveyor/ci/master/scripts/enable-rdp.ps1'))
-matrix:
-  fast_finish: true
-build_script:
-- powershell ci\build.ps1
-after_build:
-- ps: |
-    if (Test-Path $env:GCOV_ERROR_FILE) {
-      Get-Content $env:GCOV_ERROR_FILE -Head 10
-      Get-Content $env:GCOV_ERROR_FILE -Tail 10
-    } else {
-      write-host "no GCOV_ERROR_FILE"
-    }
-cache:
-- C:\projects\nvim-deps -> third-party\**
-artifacts:
-- path: build/Neovim.zip
-- path: build/bin/nvim.exe