- Retire long time unused (basically always unused) sys__umtx_lock()
and sys__umtx_unlock() syscalls
- struct umtx and their supporting definitions
- UMUTEX_ERROR_CHECK flag
- Retire UMTX_OP_LOCK/UMTX_OP_UNLOCK from _umtx_op() syscall
__FreeBSD_version is not bumped yet because it is expected that further
breakages to the umtx interface will follow up in the next days.
However there will be a final bump when necessary.
Sponsored by: EMC / Isilon storage division
Reviewed by: jhb
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