Simplify hasClassifier

We can remove all branching from this method and return the check
directly.

src/main/java/org/apache/maven/plugins/jar/AbstractJarMojo.java

@@ -335,13 +335,7 @@ private boolean projectHasAlreadySetAnArtifact()
      */
     protected boolean hasClassifier()
     {
-        boolean result = false;
-        if ( getClassifier() != null && getClassifier().trim().length() > 0 )
-        {
-            result = true;
-        }
-
-        return result;
+        return getClassifier() != null && getClassifier().trim().length() > 0;
     }
 
     private String[] getIncludes()