Revert dotnet/source-build-externals code flow

Author: Jason Zhai

eng/Version.Details.xml

@@ -2,9 +2,9 @@
 <Dependencies>
   <ProductDependencies>
     <!-- Intermediate is necessary for source build. -->
-    <Dependency Name="Microsoft.SourceBuild.Intermediate.source-build-externals" Version="9.0.0-alpha.1.24575.1">
+    <Dependency Name="Microsoft.SourceBuild.Intermediate.source-build-externals" Version="9.0.0-alpha.1.24515.2">
       <Uri>https://github.com/dotnet/source-build-externals</Uri>
-      <Sha>ab469606a3e6b026dcac301e2dab96117c94faeb</Sha>
+      <Sha>659bf534d9fbf673493b821be99df12032277549</Sha>
       <SourceBuild RepoName="source-build-externals" ManagedOnly="true" />
     </Dependency>
     <!-- Intermediate is necessary for source build. -->