package/ci: Chocolatey, go away.

package/ci/appveyor.yml

@@ -40,7 +40,11 @@ environment:
     PYTHON: 36
 
 install:
-- cinst ninja
+# Ninja. `cinst ninja` started 503ing in late November 2019 and wasn't really
+# reliable before either. So install by hand, as that's reliable always.
+- IF NOT EXIST %APPVEYOR_BUILD_FOLDER%\ninja-win.zip appveyor DownloadFile https://github.com/ninja-build/ninja/releases/download/v1.9.0/ninja-win.zip
+- 7z x ninja-win.zip -oC:/tools/ninja
+
 # pip is in Scripts
 - set PATH=C:/tools/ninja;C:/Python%PYTHON%-x64;C:/Python%PYTHON%-x64/Scripts;%PATH%
 - pip3 install coverage codecov