Remove Appveyor builds

appveyor.yml

-install:
-  - ps: |
-      if ($env:PLATFORM -eq "x86") {
-        Start-FileDownload 'https://static.rust-lang.org/dist/rust-1.0.0-i686-pc-windows-gnu.exe' -FileName rust.exe
-      } else {
-        Start-FileDownload 'https://static.rust-lang.org/dist/rust-1.0.0-x86_64-pc-windows-gnu.exe' -FileName rust.exe
-      }
-  - rust.exe /VERYSILENT /NORESTART /DIR="C:\Program Files\Rust"
-  - SET PATH=%PATH%;C:\Program Files\Rust\bin
-  - rustc -vV
-  - cargo -V
-  - git submodule update --init --recursive
-
-platform:
-  - x86
-  - x64
-
-build: false
-
-test_script:
-  - cargo test --verbose