Remove CPD attribute on DiaSymReader dependency (#68523)

This breaks coherency, because roslyn @ 5d10d42 does not have a dependency on DiaSymReader, so this coherency restriction is unresolvable.

I don't think this was intended.

Furthermore, even if roslyn did have such a dependency, it would freeze this version in place, because in order to update DiaSymReader, you would have to first make it incoherency (manually edit the version), then immediately flow roslyn to itself. Otherwise, Maestro would simply change things back.

eng/Version.Details.xml

@@ -28,7 +28,7 @@
       <Sha>3f43bf1b2dead2cb51f20dc47f6dfd7981248820</Sha>
       <SourceBuild RepoName="sourcelink" ManagedOnly="true" />
     </Dependency>
-    <Dependency Name="Microsoft.DiaSymReader" Version="2.0.0" CoherentParentDependency="Microsoft.Net.Compilers.Toolset">
+    <Dependency Name="Microsoft.DiaSymReader" Version="2.0.0">
       <Uri>https://github.com/dotnet/symreader</Uri>
       <Sha>27e584661980ee6d82c419a2a471ae505b7d122e</Sha>
     </Dependency>