remove last remnants of cassandra (#20)

Author: jonenst

src/test/resources/logback-test.xml

@@ -8,7 +8,6 @@
     <root level="info">
         <appender-ref ref="STDOUT"/>
     </root>
-    <logger name="io.netty.channel.AbstractChannelHandlerContext" level="error"/>
     <!--
         suppress unreadable huge logs..
     -->