BUG#31650096: MYSQL SERVER HEAP-USE-AFTER-FREE IN TRANS_SAVEPOINT

ANALYSIS:
=========
During Bootstrap, while executing the statements from sql
file passed to the init-file server option, transaction
mem_root was being freed for every statement. This creates
an issue with multi statement transactions especially when a
statement in the transaction has to access the memory used
by the previous statement in the transaction.

FIX:
====
Transaction mem_root is freed whenever a transaction is
committed or rolled-back. Hence explicitly freeing it is not
necessary in the bootstrap implementation.

Change-Id: I40f71d49781bf7ad32d474bb176bd6060c9377dc

sql/sql_parse.cc

@@ -811,7 +811,6 @@ static void handle_bootstrap_impl(THD *thd)
 
     thd->reset_kill_query();  /* Ensure that killed_errmsg is released */
     free_root(thd->mem_root,MYF(MY_KEEP_PREALLOC));
-    free_root(&thd->transaction.mem_root,MYF(MY_KEEP_PREALLOC));
     thd->lex->restore_set_statement_var();
   }