NIO: carve away more of `System.swift` on Windows (#1669)
NIO: carve away more of `System.swift` on Windows (#1669)

`System` interfaces should be considered deprecated and not be used.
This removes more of the interfaces from Windows as the socket
interfaces are now part of BSDSocketAPI.

Co-authored-by: Cory Benfield <e2b4f0650e369574e9b0029c3b3893634b6d4097@apple.com>
apple/swift-nio,apple/swift-nio,apple/swift-nio,apple/swift-nio,apple/swift-nio