Remove appveyor

.appveyor.yml

@@ -1,11 +0,0 @@
-install:
-  - appveyor-retry appveyor DownloadFile https://win.rustup.rs/ -FileName rustup-init.exe
-  - if not defined RUSTFLAGS rustup-init.exe -y --default-host x86_64-pc-windows-msvc --default-toolchain nightly
-  - set PATH=%PATH%;C:\Users\appveyor\.cargo\bin
-  - rustc -V
-  - cargo -V
-
-build: false
-
-test_script:
-  - cargo test --locked