Fix maintenance hazards caused by ill-considered use of default: cases.

Remove default cases from assorted switches over ObjectClass and some
related enum types, so that we'll get compiler warnings when someone
adds a new enum value without accounting for it in all these places.

In passing, re-order some switch cases as needed to match the declaration
of enum ObjectClass.  OK, that's just neatnik-ism, but I dislike code
that looks like it was assembled with the help of a dartboard.

Discussion: https://postgr.es/m/20170512221010.nglatgt5azzdxjlj@alvherre.pgsql

Author: tglsfdc

src/backend/catalog/dependency.c

@@ -1204,6 +1204,10 @@ doDeletion(const ObjectAddress *object, int flags)
 			RemoveSchemaById(object->objectId);
 			break;
 
+		case OCLASS_STATISTIC_EXT:
+			RemoveStatisticsById(object->objectId);
+			break;
+
 		case OCLASS_TSPARSER:
 			RemoveTSParserById(object->objectId);
 			break;
@@ -1265,13 +1269,20 @@ doDeletion(const ObjectAddress *object, int flags)
 			DropTransformById(object->objectId);
 			break;
 
-		case OCLASS_STATISTIC_EXT:
-			RemoveStatisticsById(object->objectId);
+			/*
+			 * These global object types are not supported here.
+			 */
+		case OCLASS_ROLE:
+		case OCLASS_DATABASE:
+		case OCLASS_TBLSPACE:
+		case OCLASS_SUBSCRIPTION:
+			elog(ERROR, "global objects cannot be deleted by doDeletion");
 			break;
 
-		default:
-			elog(ERROR, "unrecognized object class: %u",
-				 object->classId);
+			/*
+			 * There's intentionally no default: case here; we want the
+			 * compiler to warn if a new OCLASS hasn't been handled above.
+			 */
 	}
 }