* RemoveTmpDirs function to tsdbutil
* Refactor db to use RemoveTmpDirs and no longer cleanup checkpoint tmp dirs
* Use RemoveTmpDirs in wlog checkpoint to cleanup all checkpoint tmp folders
* Add tests for RemoveTmpDirs
* Ensure db.Open will still cleanup extra temporary checkpoints
Signed-off-by: Kyle Eckhart <kgeckhart@users.noreply.github.com>