Remove unneeded DiagnosticSource content (#112116)

The IL link file was getting included as unnecessary content in transitive dependent projects which caused confusion.

Fixes #112110

Author: noahfalk

src/libraries/System.Diagnostics.DiagnosticSource/src/System.Diagnostics.DiagnosticSource.csproj

@@ -25,7 +25,7 @@ System.Diagnostics.DiagnosticSource</PackageDescription>
 
   <ItemGroup>
     <ILLinkSubstitutionsXmls Include="ILLink/ILLink.Substitutions.Shared.xml" />
-    <Content Include="ILLink\ILLink.Descriptors.LibraryBuild.xml" />
+    <None Include="ILLink\ILLink.Descriptors.LibraryBuild.xml" />
   </ItemGroup>
 
   <ItemGroup>