dotnet: stop logging nuget-to-json to deps.out

stderr now propagates through msbuild in VMR builds, so this shouldn't
be necessary.

pkgs/development/compilers/dotnet/record-downloaded-packages.proj

···
       <_NuGetToNixPackageCache Include="$(ProjectDirectory)artifacts/source-build/self/package-cache/"/>
     </ItemGroup>
     <Exec
-      Command="nuget-to-json '@(_NuGetToNixPackageCache)' >'$(ProjectDirectory)deps.json' 2>'$(ProjectDirectory)deps.out'"
+      Command="nuget-to-json '@(_NuGetToNixPackageCache)' >'$(ProjectDirectory)deps.json'"
       WorkingDirectory="$(ProjectDirectory)"
       Condition="Exists('%(Identity)')"/>
   </Target>