applier: do not print 'authenticated' message if connecting as guest

Before commit 2788dc1b ("Add APPLIER_READY state") we only printed
the 'authenticated' message to the log in case credentials were set in
the replication URI. The commit changed that: now we print the message
even in case of guest connections, when applier does not send the AUTH
command to the master at all. As a result if guest connections are not
permitted by the master, the applier will keep printing 'authenticated'
after every unsuccessful attempt to subscribe. This is misleading. Let
us revert back to the behavior we had before commit 2788dc1b.

Closes #3113