Use the dotnet included in the build image

appveyor.yml

@@ -2,17 +2,6 @@ version: '{build}'
 skip_tags: true
 image: Visual Studio 2017
 configuration: Release
-environment:
-  # Set the DOTNET_SKIP_FIRST_TIME_EXPERIENCE environment variable to stop wasting time caching packages
-  DOTNET_SKIP_FIRST_TIME_EXPERIENCE: true
-  # Disable sending usage data to Microsoft
-  DOTNET_CLI_TELEMETRY_OPTOUT: true
-install:
-  - ps: mkdir -Force ".\build\" | Out-Null
-  - ps: Invoke-WebRequest "https://raw.githubusercontent.com/dotnet/cli/rel/1.0.0/scripts/obtain/dotnet-install.ps1" -OutFile ".\build\installcli.ps1"
-  - ps: $env:DOTNET_INSTALL_DIR = "$pwd\.dotnetcli"
-  - ps: '& .\build\installcli.ps1 -InstallDir "$env:DOTNET_INSTALL_DIR" -NoPath -Version 1.0.1'
-  - ps: $env:Path = "$env:DOTNET_INSTALL_DIR;$env:Path"
 build_script:
 - ps: ./Build.ps1
 test: off