Remove frivolous and dangerous calls to .retain()

Solves issues in downstream Glowstone.

Newly created ByteBufs don't need to have .retain() called, only if you're passing a bytebuf unchanged from one handler to another. That isn't the case in any of the calls, and so there are resource leak problems in implementing projects.

Pom version change is just for ease of testing, you can revert at leisure.