Removed Java 7 backport Socket utilities (#880)

Author: exceptionfactory

src/main/java/com/hierynomus/sshj/backport/Jdk7HttpProxySocket.java

@@ -22,8 +22,6 @@
 import java.net.Socket;
 import java.util.concurrent.TimeUnit;
 
-import static com.hierynomus.sshj.backport.Sockets.asCloseable;
-
 public class SocketStreamCopyMonitor
         extends Thread {
 
@@ -43,7 +41,7 @@ public void run() {
                     await(y);
                 } catch (IOException ignored) {
                 } finally {
-                    IOUtils.closeQuietly(channel, asCloseable(socket));
+                    IOUtils.closeQuietly(channel, socket);
                 }
             }
 

src/main/java/com/hierynomus/sshj/backport/Sockets.java

@@ -29,8 +29,6 @@
 import java.net.SocketException;
 import java.util.concurrent.TimeUnit;
 
-import static com.hierynomus.sshj.backport.Sockets.asCloseable;
-
 public class LocalPortForwarder {
 
     public static class ForwardedChannel
@@ -78,7 +76,7 @@ private void startChannel(Socket socket) throws IOException {
             chan.open();
             chan.start();
         } catch (IOException e) {
-            IOUtils.closeQuietly(chan, asCloseable(socket));
+            IOUtils.closeQuietly(chan, socket);
             throw e;
         }
     }