kernel/thread_abort: Remove needless locking
kernel/thread_abort: Remove needless locking

The two APIs protected by this lock are themselves internally
synchronized.  Replace the irq_lock with a spinlock anyway, because
what I think it's doing is trying to prevent a race where something
else like an ISR or something it wakes up mucks with the thread before
this completes.  Seems fragile on SMP as it stands, but this preserves
behavior on uniprocessor architectures.

Signed-off-by: Andy Ross <c70f9a6bf6ee0cd69c8af4ce5e6b131945769315@intel.com>

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