Remove additional auth.log when enabling logging

The additional auth.log which is configured when setting
sftp_enable_logging = true simply duplicates these syslog facilities:
auth,authpriv.* and write the messages to the file
/var/log/sftp/auth.log

This duplicates the logs in multiple files and the later one is not
managed by logrotate.

Closes #1

tasks/main.yml

@@ -157,9 +157,6 @@
       # Log internal-sftp in a separate file
       :programname, isequal, "internal-sftp" -/var/log/sftp/verbose.log
       :programname, isequal, "internal-sftp" ~
-
-      # additionally write an auth log
-      auth,authpriv.*  /var/log/sftp/auth.log
   when: sftp_enable_logging
   notify: SFTP-Server | Restart rsyslog