atlasdb-client depends on rocksdbjni, a 16MB JAR file

[mglazer]

From: https://github.com/palantir/atlasdb/blob/develop/atlasdb-client/build.gradle#L77

I do not believe that atlasdb-client should have a compile dependency on rocksdb. At minimum, it should be a light dependency which doesn't require downstream consumers to pull in the dependency.