pg_createsubscriber - more logging to say if there are no pubs to drop

Hi hackers,

While reviewing pg_createsubscriber in another thread, I found some of
the current logging to be confusing. Specifically, there is one part
that drops all existing publications. Sometimes it might look like
this:

----------
pg_createsubscriber: dropping all existing publications in database "db2"
pg_createsubscriber: dropping publication "pub_exists1" in database "db2"
pg_createsubscriber: dropping publication "pub_exists2" in database "db2"
pg_createsubscriber: dropping publication "pub_exists3" in database "db2"
----------

~~~

OTOH, if there is nothing found to be dropped, then the logging just says:

----------
pg_createsubscriber: dropping all existing publications in database "db2"
----------

That's the scenario that I found ambiguous. You can't be sure from the
logs what happened:
- Were there publications found, and were they dropped silently?
- Did it not find anything to drop?

~~~

Here is a small patch to remove that doubt. Now, if there is nothing
found, the logging would look like:

----------
pg_createsubscriber: dropping all existing publications in database "db2"
pg_createsubscriber: no publications found
----------

Thoughts?

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Kind Regards,
Peter Smith.
Fujitsu Australia