re-enable categorization IT (elastic/x-pack-elasticsearch#2534)

re-enables categorization IT after fixing https://github.com/elastic/machine-learning-cpp/issues/279 upstream

Original commit: elastic/x-pack-elasticsearch@398a668125

plugin/src/test/java/org/elasticsearch/xpack/ml/integration/CategorizationIT.java

@@ -81,7 +81,6 @@ public class CategorizationIT extends MlNativeAutodetectIntegTestCase {
         client().admin().indices().prepareRefresh("*").get();
     }
 
-    @AwaitsFix(bugUrl = "https://github.com/elastic/machine-learning-cpp/issues/279")
     public void testBasicCategorization() throws Exception {
         Job.Builder job = newJobBuilder("categorization", Collections.emptyList());
         registerJob(job);