Get rid of Windows CI (Appveyor)

appveyor.yml

@@ -1,21 +0,0 @@
-environment:
-  matrix:
-  - TARGET: nightly-x86_64-pc-windows-msvc
-  - TARGET: nightly-i686-pc-windows-msvc
-  - TARGET: nightly-x86_64-pc-windows-gnu
-  - TARGET: nightly-i686-pc-windows-gnu
-install:
-  - ps: Start-FileDownload "https://static.rust-lang.org/dist/rust-${env:TARGET}.exe" -FileName "rust-install.exe"
-  - ps: .\rust-install.exe /VERYSILENT /NORESTART /DIR="C:\rust" | Out-Null
-  - ps: $env:PATH="$env:PATH;C:\rust\bin"
-  - rustc -vV
-  - cargo -vV
-build_script:
-  - cargo build
-test_script:
-  - cargo test
-  - cargo bench
-artifacts:
-  - path: target
-    name: Cargo output
-    type: zip