Replace problematic bwc indices for 2.3.1 with newly generated one.

Restore the test OldIndexBackwardsCompatibilityIT.testOldIndexes which now works fine with 2.3.1 bwc indices.

core/src/test/java/org/elasticsearch/bwcompat/OldIndexBackwardsCompatibilityIT.java

@@ -294,8 +294,7 @@ public class OldIndexBackwardsCompatibilityIT extends ESIntegTestCase {
             fail(msg.toString());
         }
     }
-
-    @AwaitsFix(bugUrl = "https://github.com/elastic/elasticsearch/issues/17514")
+    
     public void testOldIndexes() throws Exception {
         setupCluster();