Remove no-op assert statement in ClientQuerySegmentWalker (#9607)

* Remove no-op assert statement

The assert statement in ClientQuerySegmentWalker will always be true because
of the preceeding while loop which has the same condition.
This change removes dead code to fix an error reported by LGTM

* Suppress lgtm

* cleanup whitespace

server/src/main/java/org/apache/druid/server/ClientQuerySegmentWalker.java

@@ -274,8 +274,7 @@ public class ClientQuerySegmentWalker implements QuerySegmentWalker
           current = Iterables.getOnlyElement(current.getChildren());
         }
 
-        assert !(current instanceof QueryDataSource);
-
+        assert !(current instanceof QueryDataSource); // lgtm [java/contradictory-type-checks]
         current = inlineIfNecessary(current, null, subqueryRowLimitAccumulator, maxSubqueryRows, dryRun);
 
         while (!stack.isEmpty()) {