Remove unused dependency to get rid of warning.

I get always the following warning:
===
SLF4J: Class path contains multiple SLF4J bindings.
SLF4J: Found binding in [jar:file:/home/rathgeb/.m2/repository/org/slf4j/slf4j-jdk14/1.6.2/slf4j-jdk14-1.6.2.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: Found binding in [jar:file:/home/rathgeb/.m2/repository/org/slf4j/slf4j-log4j12/1.6.2/slf4j-log4j12-1.6.2.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: See http://www.slf4j.org/codes.html#multiple_bindings for an explanation.
===

Do not know, why multiple slf4j libraries are used.
slf4j-log4j12: Binding for log4j version 1.2, a widely used logging framework. You also need to place log4j.jar on your class path.
slf4j-jdk14: Binding for java.util.logging, also referred to as JDK 1.4 logging

We could disable the slf4j-log4j12 dependency (and so the log4j dependency) by using slf4j-jdk14 only.