Removing manual SDK install

Author: jbogard

appveyor.yml

@@ -5,15 +5,6 @@ branches:
   only:
   - master
 image: Visual Studio 2017
-## temporary until 2.1 sdk is installed
-install:  
-  - ps: $urlCurrent = "https://dotnetcli.blob.core.windows.net/dotnet/Sdk/2.1.300/dotnet-sdk-2.1.300-win-x64.zip"
-  - ps: $env:DOTNET_INSTALL_DIR = "$pwd\.dotnetsdk"
-  - ps: mkdir $env:DOTNET_INSTALL_DIR -Force | Out-Null
-  - ps: $tempFileCurrent = [System.IO.Path]::GetTempFileName()
-  - ps: (New-Object System.Net.WebClient).DownloadFile($urlCurrent, $tempFileCurrent)
-  - ps: Add-Type -AssemblyName System.IO.Compression.FileSystem; [System.IO.Compression.ZipFile]::ExtractToDirectory($tempFileCurrent, $env:DOTNET_INSTALL_DIR)
-  - ps: $env:Path = "$env:DOTNET_INSTALL_DIR;$env:Path" 
 nuget:
   disable_publish_on_pr: true
 build_script: