Refactor: remove redundant return and unused method from MacAuth

Change-Id: Ib65b49a62172ff3c4f3611c08544e673ec4fb93b

protocols/lisp/msg/src/main/java/org/onosproject/lisp/msg/authentication/LispMacAuthentication.java

@@ -47,7 +47,6 @@ public class LispMacAuthentication {
             algorithm = authType.getName();
         } else {
             log.warn(NOT_SUPPORT_ALGORITHM_MSG, authType.getName());
-            return;
         }
     }
 
@@ -82,13 +81,4 @@ public class LispMacAuthentication {
             throw new RuntimeException(e);
         }
     }
-
-    /**
-     * Obtains authentication algorithm.
-     *
-     * @return authentication algorithm
-     */
-    String getAlgorithm() {
-        return algorithm;
-    }
 }