Remove #include statments in various files within kern/

Remove #include statments in various files within kern/

kern/freebsd/freebsd_system.cc:
kern/freebsd/freebsd_system.hh:
kern/kernel_stats.cc:
kern/kernel_stats.hh:
kern/linux/aligned.hh:
kern/linux/linux_system.cc:
kern/linux/linux_system.hh:
kern/linux/linux_threadinfo.hh:
kern/linux/printk.cc:
kern/linux/sched.hh:
kern/linux/thread_info.hh:
kern/system_events.cc:
kern/system_events.hh:
    Remove unecessary #include statements.

--HG--
extra : convert_revision : 7e32d3b096fc92708ea45db9b172bada906024cd