Remove AppVeyor config

* Will move to another windows build platform later

appveyor.yml

@@ -1,27 +0,0 @@
-environment:
-  matrix:
-    - TARGET: x86_64-pc-windows-gnu
-      BITS: 64
-      MSYS2: 1
-    - TARGET: x86_64-pc-windows-msvc
-      BITS: 64
-    - TARGET: i686-pc-windows-gnu
-      BITS: 32
-      MSYS2: 1
-    - TARGET: i686-pc-windows-msvc
-      BITS: 32
-install:
-  - cmd: >-
-    curl -sSf -o rustup-init.exe https://win.rustup.rs/ &
-    rustup-init.exe -y --default-host %TARGET% &
-    set PATH=%PATH%;C:\Users\appveyor\.cargo\bin &
-    if defined MSYS2 set PATH=C:\msys64\mingw%BITS%\bin;%PATH% &
-    rustc -V &
-    cargo -V
-build: false
-test_script:
-  - cargo build --verbose --all
-  - cargo test --verbose --all
-branches:
-  only:
-    - master