Runtime: System.Data.SqlClient still uses the non-generic collections

A quick GitHub search shows that System.Collections.Specialized and System.Data.SqlClient are the only non-test assemblies still dependent on the non-generic collections. While it's kind of inevitable for the specialized collections since it contains a lot of legacy code, it appears from this PR that we can remove System.Collections.NonGeneric from the SqlClient implementation, since it's not exposed to callers.

This is a tracking issue I'm opening up to remove the dependency from SqlClient.