Remove TypeForwardedFrom attributes for System and System.Core

Remove TypeForwardedFrom attributes for System and System.Core

These assemblies don't exist in .NET Core.  Having these attributes on serializable types causes deserialization for such types to fail, as it attempts to load the assembly from which they were forwarded.

Commit migrated from https://github.com/dotnet/coreclr/commit/97464a7c614cea28c9f526fe82c68d1a676ac964