Bonsai is broken

[LourensVeen]

Describe the bug
Bonsai does not currently compile in AMUSE.

There are currently two versions of Bonsai in the AMUSE community codes, bonsai and bonsai2. These are an older and a newer version of Bonsai. (Note: bonsai2 is not Bonsai2!) Neither compile with modern CUDA versions because of treecode/Bonsai#51.

Since this has been fixed upstream, we probably just need to upgrade to the latest version. I also propose to remove bonsai2 (possibly replacing it with a placeholder to tell people to switch back to bonsai if their scripts fail, or a redirect) and just make bonsai the latest version, since there's no point in having broken old versions lying around.