Begin snipping out the lists of specific devices from the Hardware

Begin snipping out the lists of specific devices from the Hardware
Notes.  These duplicate information that ideally should live in the
manual pages for individual drivers, and can easily become
out-of-date.  (This in fact is already the case.)

Hypertext versions of the hardware notes already contain links to
on-line versions of the manual pages.

The first two drivers to get this treatment are amr(4) and aac(4).

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