htrace-core currently depends on Guava. It seems like there are a few Guava types exposed in public interfaces too. This is unfortunate because Guava has a history of making non-backwards compatible changes without changing the namespace of the library. So we could end up locked to a specific (old) version of Guava due to this. It also interacts poorly with the shading we're doing. We should just remove guava as a depdency so we don't have to worry about this issue in the future.