Removed /2 of InnoDB ref_per_key[] estimates

The original code was there to favor index search over table scan.
This is not needed anymore as the cost calculations for table scans
and index lookups are now more exact.

mysql-test/main/subselect_innodb.test

@@ -1,5 +1,6 @@
 -- source include/no_valgrind_without_big.inc
 -- source include/have_innodb.inc
+-- source include/have_sequence.inc
 
 # Note: the tests uses only non-semijoin subqueries so semi-join switch
 #       settings are not relevant.
@@ -568,6 +569,11 @@ from
 --echo # MDEV-6081: ORDER BY+ref(const): selectivity is very incorrect (MySQL Bug#14338686)
 --echo #
 
+
+# Table t2 has 100 equal values / key value, which causes it to prefer index scan instead of ref
+# Fix it by adding more different values to key1
+insert into t2 select seq,seq,seq from seq_10000_to_11000;
+
 alter table t2 add key2 int;
 update t2 set key2=key1;
 alter table t2 add key(key2);
@@ -583,6 +589,14 @@ explain select
     ORDER BY t2.key2 ASC LIMIT 1)
 from 
   t1;
+select 
+   (SELECT 
+      concat(id, '-', key1, '-', col1)
+    FROM t2
+    WHERE t2.key1 = t1.a
+    ORDER BY t2.key2 ASC LIMIT 1)
+from 
+  t1;
 
 drop table t1,t2;