Revert "exit1(): Revert sparc64 workaround"

This reverts commit 96c76d930656f13d3c041dc8d8f2fc3dd1e5e05a.

There are other relatively common reasons why init might get killed
during reboot, the workaround was really not sparc64-specific.

Discussed with: marius
Sponsored by: The FreeBSD Foundation