Remove the installation notes, which have not truly been maintained
for quite some time. All relevant content has been moved to the
installation chapter of the FreeBSD Handbook, which will be the
single source of FreeBSD installation instructions.
In addition to removing redundancy, this change also removes the last
of the machine-dependent documents in the release documentation
set (the release notes and hardware notes were unified to produce
machine-independent documents).
Approved by: re (blanket for installation notes removal)
Nods from: blackend, brueffer, simon, trhodes
No objections on: doc@
Helpful hints from: blackend