Revert "Finish fixing Zygote descriptor leakage problem"

This reverts commit 30b46547b29b277218e9431a400b28a8c2e7d18c.
Revert "[1/2] Speed up booting on multicore devices."

This reverts commit 04bb5ddc3f8e5686dba6f471d4b7702114429a43.