BUG/MINOR: config: Remove final '\n' in error messages

Because error messages are displayed with appending final '\n', it's
useless to add '\n' in the message.

This patch should be backported.

[CF: An extra curly bracket was removed. On 2.9-dev it was removed by the commit
     65f18d65a ("BUG/MINOR: config: Lenient port configuration parsing"). But it
     was not backported to 2.8. Thus to avoid compilation error, it must be
     removed here]
1 file changed