Remove dotnet-preview Casks (#4902)

Casks/dotnet-preview.rb

@@ -1,17 +0,0 @@
-cask 'dotnet-preview' do
-  version '2.0.0-preview2-25407-01'
-  sha256 'a1682bbc89e931ab2a734056604985c59add9e08a1d56d7eb954cd0beab925e3'
-
-  url "https://download.microsoft.com/download/7/C/3/7C310A63-13AC-49A4-9666-4CB26388F852/dotnet-runtime-#{version}-osx-x64.pkg"
-  name '.NET Core Preview'
-  homepage 'https://www.microsoft.com/net/core#macos'
-
-  depends_on macos: '>= :sierra'
-
-  pkg "dotnet-runtime-#{version}-osx-x64.pkg"
-
-  uninstall pkgutil: 'com.microsoft.dotnet*',
-            delete:  '/etc/paths.d/dotnet'
-
-  zap trash: '~/.nuget'
-end

Casks/dotnet-sdk-preview.rb

@@ -1,17 +0,0 @@
-cask 'dotnet-sdk-preview' do
-  version '2.0.0-preview2-006497'
-  sha256 'de675118efc09f80d4f2927b791b64806e7fbbd640b56d408b92d4e6ce4b167c'
-
-  url "https://download.microsoft.com/download/6/1/B/61B3E81F-5509-48D2-BB4F-5189E23CD29A/dotnet-sdk-#{version}-osx-x64.pkg"
-  name '.NET Core SDK Preview'
-  homepage 'https://www.microsoft.com/net/core#macos'
-
-  depends_on macos: '>= :sierra'
-
-  pkg "dotnet-sdk-#{version}-osx-x64.pkg"
-
-  uninstall pkgutil: 'com.microsoft.dotnet*',
-            delete:  '/etc/paths.d/dotnet'
-
-  zap trash: '~/.nuget'
-end