fix comment of reinitializer

[zhiqiangxu]

initializer modifier can't be nested, either. So it's not a difference.

The comment of initializer says:

 * Similar to `reinitializer(1)`, except that in the context of a constructor an `initializer` may be invoked any
 * number of times. This behavior in the constructor can be useful during testing and is not expected to be used in
 * production.

This PR makes the comment of reinitializer consistent with that of initializer.