Remove nightly MyGet feed

Author: ronaldbarendse

src/Directory.Build.props

@@ -19,10 +19,6 @@
         <PackageReference Include="Microsoft.CodeAnalysis.PublicApiAnalyzers" Version="3.3.3" PrivateAssets="All" />
         <PackageReference Include="StyleCop.Analyzers" Version="1.2.0-beta.435" PrivateAssets="All" />
     </ItemGroup>
-
-    <PropertyGroup>
-        <RestoreAdditionalProjectSources>https://www.myget.org/F/umbraconightly/api/v3/index.json</RestoreAdditionalProjectSources>
-    </PropertyGroup>
 
     <!-- SourceLink -->
     <PropertyGroup>