Add comment and remove unused imports

Author: dimitris-athanasiou

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ml/job/config/DetectionRule.java

@@ -18,7 +18,6 @@
 import org.elasticsearch.xpack.core.ml.utils.ExceptionsHelper;
 
 import java.io.IOException;
-import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.EnumMap;

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ml/job/config/Operator.java

@@ -12,8 +12,6 @@
 
 import java.io.IOException;
 import java.util.Locale;
-import java.util.regex.Matcher;
-import java.util.regex.Pattern;
 
 /**
  * Enum representing logical comparisons on doubles

x-pack/qa/rolling-upgrade/src/test/resources/rest-api-spec/test/old_cluster/30_ml_jobs_crud.yml

@@ -175,7 +175,7 @@
 
   - skip:
       version:  " - 6.1.99"
-      reason:   "Rules replaced by custom_rules on 6.4.0"
+      reason:   "This creates a job with the same name as the rules job to ensure that job is not missing in the upgraded cluster; also some of the rule fields were deprecated in 6.2 so we using the dummy from 6.2 onwards"
 
   - do:
       xpack.ml.put_job: