remove local_lib (held jars checked into the code itself)

[pdurbin]

We added local_lib in 13b7ff0 but as part of the 6.0 release we've been working on removing it (by finding jars on Maven Central or putting them there). Only one library remains! Once it's gone, we can remove these lines from the parent pom:

    <repository>
        <id>dvn.private</id>
        <name>Local repository for hosting jars not available from network repositories.</name>
        <url>file://${project.basedir}/local_lib</url>
    </repository>