Fix typos in logback.xml configuration files.

[priornix]

Correct syntax for logback loggers should be <appender-ref> elements instead of <AppenderRef>, which does not work. This can be checked with <configuration debug="true">

https://logback.qos.ch/manual/configuration.html

[priornix]

Originally, 8c2eabd fixed the appenders to the correct syntax. However, this will result in duplicate messages, since appenders are additive in nature.

The original config file used <AppenderRef> which appears to work, because <AppenderRef> is an invalid element and logback basically ignored it, thus there were no duplicate log messages.

To avoid confusion, <AppenderRef> should be removed, as
i) it is invalid syntax
ii) it can mislead developers to think that <AppenderRef> is also valid syntax, which I had thought initially, until I looked into why my other logger's appender was not working and discovered the truth from logback's documentation.

[priornix]

Last commit 757ec65 changes <logger ...></logger> to <logger ... /> to reduce verbosity since there are no child elements. Also, neatly align the output so that they are no extra newlines.

[yogthos]

Perfect, thanks for getting this cleaned up.