- kthread's don't have p_textvp set to anything, so replace code that   dealt with that possibility with a KASSERT(). - No need to set P_SYSTEM, kthread_create() does that for us.
- kthread's don't have p_textvp set to anything, so replace code that
  dealt with that possibility with a KASSERT().
- No need to set P_SYSTEM, kthread_create() does that for us.

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