LogicalChanges* and LogicalSubxact* wait events are never reported

Hi,

When I read the documents and source code of wait evens,
I found that the following wait events are never reported.

* LogicalChangesRead: Waiting for a read from a logical changes file.
* LogicalChangesWrite: Waiting for a write to a logical changes file.
* LogicalSubxactRead: Waiting for a read from a logical subxact file.
* LogicalSubxactWrite: Waiting for a write to a logical subxact file.


The wait events are introduced in the following patch.

 Add support for streaming to built-in logical replication.
 Amit Kapila on 2020/9/3 11:24:07
 464824323e57dc4b397e8b05854d779908b55304

I read the above discussion and found the wait events were reported at first.
But they seemed to be removed because they are not necessary because
BufFileWrite/BufFileRead are enough([1]).


If my understanding is right, it's better to remove them since they make
users confused. Please see the attached patch. I confirmed that to make
check-world passes all tests.

[1]
https://www.postgresql.org/message-id/CAA4eK1JV37jXUT5LeWzkBDNNnSntwQbLUZAj6m82QMiR1ZuuHQ%40mail.gmail.com

Regards,
-- 
Masahiro Ikeda
NTT DATA CORPORATION