Move vcpkg_windows.txt to azure-devops. (#262)

`azure-devops/run_build.yml` is the only thing that uses
`vcpkg_windows.txt`, so I don't believe that it belongs
in the root of the repo.

azure-devops/run_build.yml

@@ -8,7 +8,7 @@ jobs:
 
   variables:
     vcpkgLocation: '$(Build.SourcesDirectory)/vcpkg'
-    vcpkgResponseFile: $(Build.SourcesDirectory)/vcpkg_windows.txt
+    vcpkgResponseFile: $(Build.SourcesDirectory)/azure-devops/vcpkg_windows.txt
   steps:
     - checkout: self
       submodules: recursive