bug#9404: etc/MACHINES has obsolete information

[Dan Nicolaescu]

The most of the first few sections in etc/MACHINES have obsolete
information.

** Alpha (DEC) running GNU/Linux (alpha-dec-linux-gnu)
actually talks about using the DEC compiler which was running on OSF/1,
which is not supported anymore.

** HP 9000 series 700 
** IBM RS/6000 (rs6000-ibm-aix*)
** Iris 4D (mips-sgi-irix6.*)
** Sun 4 (sparc), Sun 386
talk about old releases and old compilers that are very likely not in
use anymore.
** Intel 386 (i386-*-freebsd,      i386-*-linux-gnu
Very old info.

Instead of carrying this old info for ancient stuff, just remove it and
have users report problems here.