Remove agent.os demands on windows ci (#621)

* Remove agent.os demands as this queue has only Windows_NT machines

* Bump parallel to 4

* Set parallel to 99 per PR feedback

.vsts-dotnet-ci.yml

@@ -11,5 +11,3 @@ phases:
     buildScript: build.cmd
     queue:
       name: Hosted VS2017
-      demands:
-        - agent.os -equals Windows_NT

build/ci/phase-template.yml

@@ -13,7 +13,7 @@ phases:
       ${{ if ne(parameters.dockerImage, '') }}:
         _PREVIEW_VSTS_DOCKER_IMAGE: ${{ parameters.dockerImage }}
     queue:
-      parallel: 2
+      parallel: 99
       matrix:
         Build_Debug:
           _configuration: Debug