Remove unnecessary `reboot()` header includes from `AdminUtils` (#1013)
Remove unnecessary `reboot()` header includes from `AdminUtils` (#1013)

This change removes the extraneous include of Linux-specific header files for the `reboot` syscall. We were using the common BSD variant of it anyway, which is more portable and requires just ` <unistd.h>` and  `<sys/reboot.h>`.
As a side effect, this class now builds on MacOS as well.

Closes #846 #843 
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