AR: Remove comment about privspec/CSR behavior

From Greg: "... why is this non-normative comment even necessary?  It's
directly consistent with 1.12, and it's compatible with 1.13 which
allows for trapping and just doesn't require it.  In other words, wrt
1.13, this trapping mandate by Debug 1.0 doesn't conflict with Priv
1.13.  And that allows Debug 1.0 to come along and tighten what is
allowed by 1.13."