remove System.Collections.Immutable package

no longer requires direct reference

Author: arturcic

src/GitVersion.Testing/GitVersion.Testing.csproj

@@ -17,7 +17,6 @@
         <InternalsVisibleTo Include="GitVersion.MsBuild.Tests" />
     </ItemGroup>
     <ItemGroup>
-      <PackageReference Include="System.Collections.Immutable" VersionOverride="10.0.1" />
       <ProjectReference Include="..\GitVersion.Core\GitVersion.Core.csproj" />
     </ItemGroup>
 </Project>