graphics/cbonsai: Update to latest commit

Whilst here, remove the do-build target and cleanup a little.

Changes: https://gitlab.com/jallbrit/cbonsai/-/commit/e1070054e5bf5c30056cd31f01e8ecc8df8f02cd
Approved by: tcberner (mentor)
Differential Revision: https://reviews.freebsd.org/D28517