Remove System.Memory since it is built into the runtime (Azure#50576)

* remove System.Memory since it is built into the runtime

* Update eng/Directory.Build.Common.targets

Co-authored-by: Copilot <[email protected]>

* Update Directory.Build.Common.targets

---------

Co-authored-by: Copilot <[email protected]>

Author: m-redding

eng/Directory.Build.Common.targets

@@ -105,6 +105,7 @@
   <ItemGroup Condition="$([MSBuild]::IsTargetFrameworkCompatible('$(TargetFramework)', 'net6.0'))">
     <PackageReference Remove="System.Buffers" />
     <PackageReference Remove="System.Diagnostics.DiagnosticSource" />
+    <PackageReference Remove="System.Memory" />
     <PackageReference Remove="System.Net.Http" />
     <PackageReference Remove="System.Numerics.Vectors" />
     <PackageReference Remove="System.Text.Encodings.Web" />