Remove redundant final modifier

Since EnginePlugin is an interface, a final modifier on a parameter in a
method declared there is redundant.

core/src/main/java/org/elasticsearch/plugins/EnginePlugin.java

@@ -37,6 +37,6 @@ public interface EnginePlugin {
      *
      * @return an optional engine factory
      */
-    Optional<EngineFactory> getMaybeEngineFactory(final IndexSettings indexSettings);
+    Optional<EngineFactory> getMaybeEngineFactory(IndexSettings indexSettings);
 
 }