Remove outdated information from the FreeBSD/MIPS platform page: it is
unlikely we will ever support SGI MIPS, we're certainly not actively
targeting it.  Make the page more similarly match other platform pages.

Still to do: add more details of platforms we do support.


git-svn-id: svn+ssh://svn.freebsd.org/doc/head@45598 c2e8774f-c49f-e111-b436-862b2bbc8956