Document pt-table-checksum privileges

This is no longer needed due to bug 916168.

The documentation for this tool needs to include the minimum necessary privileges to run the queries on a master with no replicas attached, as well as the privileges that might be needed on the replicas to inspect their status. It would be nice if this documentation were broken out by functional area, so that if someone creates the checksum table manually, and wants to run the tool without the create table privilege, the documentation guides them and how they can do that.

In addition, we need to document that the tool works with all storage engines.

Here's a start which may not be correct:

It requires SELECT on all the tables and databases, and requires
INSERT, UPDATE, and DELETE on the table mentioned in --replicate if
you're using that. If you want it to auto-create the --replicate
table, naturally it needs that permission, but you can just create it
yourself too.

Another report:

On the master (where mk-table-checksum is run):

PROCESS
SUPER
SELECT on relevant tables to check
INSERT, UPDATE, DELETE, SELECT on table specified with --replicate

On the slave:

PROCESS
REPLICATION CLIENT
REPLICATION SLAVE
SELECT on table specified with --replicate