After ACCUMULO-1242 is complete, we should not have any more direct usage of log4j or any other particular slf4j implementation. As such, we should mark log4j (and any other slf4j implementations) as optional in the dependencies section of the POM.
"Optional" dependencies in Maven are not automatically inherited transitively when other projects depend on ours. This is important, because if somebody writes a client application which depends on Accumulo code, we should not be forcing that application into a particular logging implementation. Marking it optional is preferable to forcing them to exclude the transitive dependencies in order to provide their own. It will also prevent conflicts when they have dependencies on other projects, which require a particular conflicting implementation of slf4j.