os: implement cp for nix

vlib/net/socket.v

@@ -62,12 +62,8 @@ fn C.send() int
 
 fn C.recv() int
 
-fn C.read() int
-
 fn C.shutdown() int
 
-fn C.close() int
-
 fn C.ntohs() int
 
 fn C.getsockname() int

vlib/net/websocket/io.v

@@ -1,7 +1,5 @@
 module websocket
 
-fn C.write() int
-
 fn (mut ws Client) write_to_server(buf voidptr, len int) int {
 	mut bytes_written := 0
 	ws.write_lock.lock()