Refactoring of replication commands using printsimple

Hi all,

This is a follow up of the refactoring that has been discussed in the
thread to increase the default size of WAL segments:
https://www.postgresql.org/message-id/CAB7nPqQ4hyNrLq+W1JrrYVSySOxuQa40PYb2Uw5UQkKaG4hong@mail.gmail.com

The discussion has resulted in the creation of a84069d9 that has
introduced a new DestReceiver method called printsimple that does not
need any catalog access. After some investigation, I have noticed that
a couple of messages used in the replication protocol could be
refactored as well:
- IDENTIFY_SYSTEM
- TIMELINE_HISTORY
- CREATE_REPLICATION_SLOT
This results in the following code reduction:
 3 files changed, 115 insertions(+), 162 deletions(-)

A commit fest entry has been created:
https://commitfest.postgresql.org/13/978/

Thanks,
-- 
Michael