Fix Workspaces.MSBuild project to use minimal MSBuild syntax

src/Workspaces/Core/MSBuild/Workspaces.MSBuild.csproj

 <?xml version="1.0" encoding="utf-8"?>
 <!-- Copyright (c)  Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information. -->
-<Project DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
-  <Import Project="..\..\..\..\build\Targets\SettingsSdk.props" />
+<Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <Platform Condition="'$(Platform)' == ''">AnyCPU</Platform>
     <PlatformTarget>AnyCPU</PlatformTarget>
@@ -12,8 +11,6 @@
     <TargetFramework>net46</TargetFramework>
     <DefineConstants>$(DefineConstants);WORKSPACE_MSBUILD</DefineConstants>
   </PropertyGroup>
-  <PropertyGroup Condition="'$(Configuration)|$(Platform)' == 'Debug|AnyCPU'" />
-  <PropertyGroup Condition="'$(Configuration)|$(Platform)' == 'Release|AnyCPU'" />
   <ItemGroup>
     <Compile Include="..\..\..\Compilers\Shared\DesktopAnalyzerAssemblyLoader.cs">
       <Link>InternalUtilities\DesktopAnalyzerAssemblyLoader.cs</Link>
@@ -58,5 +55,4 @@
     <InternalsVisibleToTest Include="Roslyn.VisualStudio.Test.Utilities2" />
     <InternalsVisibleToMoq Include="DynamicProxyGenAssembly2" />
   </ItemGroup>
-  <Import Project="..\..\..\..\build\Targets\Imports.targets" />
 </Project>
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