Rollback to BuildTools 2.1.0-preview1-15551

This reverts commit d1eabf8dfa998277e2824274fb50c52aa7800b95.

Razor and MVC are broken by the new SDK

build/dependencies.props

@@ -97,7 +97,7 @@
   <!-- ASP.NET Core Tools feed -->
   <PropertyGroup>
     <AspNetCoreToolsFeed>https://dotnet.myget.org/F/aspnetcore-tools/api/v3/index.json</AspNetCoreToolsFeed>
-    <InternalAspNetCoreSdkPackageVersion>2.1.0-preview1-15557</InternalAspNetCoreSdkPackageVersion>
+    <InternalAspNetCoreSdkPackageVersion>2.1.0-preview1-15551</InternalAspNetCoreSdkPackageVersion>
   </PropertyGroup>
 
   <ItemGroup>

korebuild-lock.txt

@@ -1,2 +1,2 @@
-version:2.1.0-preview1-15557
-commithash:eaef791ebeccb3984515837b5eded474d66de048
+version:2.1.0-preview1-15551
+commithash:8fad9553b48533fddbb16a423ea55b9710ea2e63