chore: Use IoSlice's Copy impl to clean up some repetitive code (#2875)
chore: Use IoSlice's Copy impl to clean up some repetitive code (#2875)

As we go into 0.3 we no longer need to support older versions of Rust where
IoSlice did not implement Copy and Clone, so we can more easily initialize the
IoSlice array in net::tcp::stream.

Co-authored-by: Bryan Donlan <8608f8155b6502a321ec6da8ce351e54842eec96@amazon.com>
tokio-rs/tokio,tokio-rs/tokio