Before this fix,
- "memory/%" instruments could be configured with
  TIMED='YES' or TIMED='NO' in table setup_instrument.
- "memory/performance_schema/%" instruments could be configured with
  ENABLED='YES' or ENABLED='NO' in table setup_instrument.

This does not make sense, because:
- memory instruments in general are never timed,
- performance_schema builtin memory instruments in particular can not be disabled

With this fix,
- "memory/%" instruments are never timed.
- "memory/performance_schema/%" instruments are never disabled.

This fix avoids confusion, by displaying more truthfully in table
setup_instrument what the server actually does with the memory
instrumentation.