MDEV-17658 change the structure of mysql.user table

Implement User_table_json.
Fix scripts to use mysql.global_priv.
Fix tests.

mysql-test/suite/binlog/t/binlog_stm_binlog.test

@@ -3,10 +3,6 @@
 let collation=utf8_unicode_ci;
 --source include/have_collation.inc
 
---disable_warnings
-drop table if exists t1;
---enable_warnings
-
 # REQUIREMENT
 #   replace_regex should replace output of SHOW BINLOG EVENTS