About dependencies that are not used in code

[Jialin Qiao <qi...@apache.org>]

Hi,

Recently I checked the lib of our binary release and corresponding
dependencies in pom.

I found that the jna in pom of CLI is not imported in any class, so I
submit a PR to remove it.
Later Haonan told me that it is used only on windows, not in code.

So I'd like to remind that if some dependency is not used in code but for
other reasons, please add some comments above the dependency to avoid being
removed by others negligently.

Thanks,
Jialin Qiao