These resources were added to the ARM64 subfolder in dotnet#10023,
but I don't think they're needed: there's no .NET Framework 3.5
for ARM64 and `MSBuildTaskHost.exe` isn't in the ARM64 folder
itself, so I think we can remove these files.

There was also a build race condition involving the .resources.dll
files, which is how I found this. The `Arm64ProjectReference`
wasn't enough to get them built.