Fix null pointer.

src/main/java/net/schmizz/sshj/transport/verification/OpenSSHKnownHosts.java

@@ -376,11 +376,6 @@ public class OpenSSHKnownHosts
             return saltyBytes;
         }
 
-        @Override
-        public String getLine() {
-            return null;
-        }
-
         @Override
         protected String getHostPart() {
             return hashedHost;