* Update License

Update License to match https://github.com/dotnet/arcade/commit/1e49672184ca450fbf3ea73e1122924ed4bb2ccc
and fix issue with https://github.com/dotnet/iot/pull/339

* define only PackageLicenseExpression, update SDK to 2.1.503

* add copyright back

* remove Copyright from .props

* Get latest version of arcade to get new licensing changes