Remove unused coreos/go-etcd fork from third_party

The only usage of this was removed via #18635

third_party/forked/coreos/go-etcd/etcd/client.go

@@ -1,32 +0,0 @@
-package etcd
-
-import (
-	"errors"
-	"net"
-	"time"
-)
-
-// dial attempts to open a TCP connection to the provided address, explicitly
-// enabling keep-alives with a one-second interval.
-func Dial(network, addr string) (net.Conn, error) {
-	conn, err := net.DialTimeout(network, addr, time.Second)
-	if err != nil {
-		return nil, err
-	}
-
-	tcpConn, ok := conn.(*net.TCPConn)
-	if !ok {
-		return nil, errors.New("Failed type-assertion of net.Conn as *net.TCPConn")
-	}
-
-	// Keep TCP alive to check whether or not the remote machine is down
-	if err = tcpConn.SetKeepAlive(true); err != nil {
-		return nil, err
-	}
-
-	if err = tcpConn.SetKeepAlivePeriod(time.Second); err != nil {
-		return nil, err
-	}
-
-	return tcpConn, nil
-}