Free unused JOINs early even if using subqueries.

sql/sql_select.cc:
  According to the conclusion made in the previous patch, we can widen
  the range of cases when JOINs are fully freed early, and include 
  subqueries to it.

sql/sql_select.cc

@@ -5902,8 +5902,7 @@ void JOIN::join_free(bool full)
     Optimization: if not EXPLAIN and we are done with the JOIN,
     free all tables.
   */
-  full= full || (!select_lex->uncacheable && !thd->lex->subqueries &&
-                 !thd->lex->describe);
+  full= full || (!select_lex->uncacheable && !thd->lex->describe);
 
   cleanup(full);