Remove scriptRemoved() method

Related to elastic/elasticsearch@18572

Original commit: elastic/x-pack-elasticsearch@ec43b58111

elasticsearch/x-pack/watcher/src/test/java/org/elasticsearch/script/SleepScriptEngine.java

@@ -64,10 +64,6 @@ public class SleepScriptEngine implements ScriptEngineService {
         return null;
     }
 
-    @Override
-    public void scriptRemoved(@Nullable CompiledScript script) {
-    }
-
     @Override
     public void close() throws IOException {
     }