This also happened to me a few weeks ago. The underlying problem seems to be that the uninstall script fails because it tries to call sage-dist-helpers, but cannot find it. This file has recently been moved from src/bin to build/bin, which the uninstall script cannot know about. Once upgraded to Gap 4.10.2.p0, it points to the new location of sage-dist-helpers, so this particular problem should not happen again.
This has also been reported on devel [1,2] and might affect more Mac users when upgrading to 8.9. Perhaps a copy of sage-dist-helpers could be added back to src/bin for some deprecation period?  https://groups.google.com/forum/#!topic/sage-devel/cdw793St6cE  https://groups.google.com/forum/#!topic/sage-devel/h-hXvO2fxgc -- You received this message because you are subscribed to the Google Groups "sage-release" group. To unsubscribe from this group and stop receiving emails from it, send an email to sage-release+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/sage-release/a4cd4e30-5b2b-4890-a744-9776b2ec2223%40googlegroups.com.