[source-build] Do not include current RID in runtime pack list when building from source

Original issues: https://github.com/dotnet/source-build/pull/1231, https://github.com/dotnet/source-build/issues/1202, https://github.com/dotnet/source-build/issues/1232.

Source-build currently uses [this patch](https://github.com/dotnet/source-build/blob/9bb1c85e13bc44f8a0c6de41779366da6e5c61ac/patches/core-sdk/0003-Don-t-add-target-rid-to-NetCoreRuntimePackRids.patch) to remove the currently building RID from this list. Prior to the patch, this was causing issues with RID-specific publish and ReadyToRun. We should figure out a good fix for this that isn't just hardcoding the RID list.