remove recommendation Restrict Host for 'root'@% to root@SpecificDNSorIp

[grooverdan]

Reasons for removal:

• container environment pretty much exclusively use '%' for grants and the network isn't known (by mysql/mariadb container producers), and even a local environment would keen it this way and apply limits in their docker swarm or kubernetes configuraiton.

  UPDATE mysql.user SET host ='SpecificDNSorIp' WHERE user='root' AND host ='%'; FLUSH PRIVILEGES;

Why this is a horrible suggestion (to which detailed, but incomplete, work around can be written if still desired):

• Procedures, events, triggers, functions (and possibly others) objects connected to root@% become instantly invalid.
• Encourages too much direct manipulation of mysql system tables.
• Won't work on MariaDB-10.4+

[grooverdan]

seems I've missed the existence of https://dev.mysql.com/doc/refman/5.6/en/rename-user.html which solves all but the container environment cases.