Before this fix, the privileges in the performance schema
allowed the user to:
- CREATE any performance schema table
- DROP / TRUNCATE any performance schema table

Allowing these operations was necessary for the
install and upgrade SQL scripts.

With the recent implementation of:
WL#7900 New DD: Support flexible creation
  and versioning of virtual P_S tables
WL#8879 PERFORMANCE SCHEMA, TABLE PLUGIN

the table creation is no longer done using a SQL CREATE TABLE statement,
but embedded in the server code itself.

As a result, allowing CREATE and DROP on performance schema tables
is no longer necessary, and privileges can be more restrictive.

With this fix,
- CREATE TABLE is never allowed to a user,
- DROP TABLE is never allowed to a user,
- TRUNCATE TABLE is only allowed for tables that supports truncation.