In principle, you should be able to type make micro_release, but this may be broken, depending on your platform. (I think that if it's broken, it will still result in a working Sage installation, just one that isn't as small as it should be.)
When you run sage micro_release, it runs the script local/bin/sage-micro-release, which among other things removes the directories devel/sage/build/temp.* and devel/sage/build/lib.*. You should be able to delete those safely by hand, if the script fails.
You can also safely remove the directory spkg/logs/. If you're sure you're not going to need to reinstall anything, you could remove spkg/standard/.