[tlbuild] pruning platforms

[Karl Berry]

We need to save space on the DVD -- turns out that
TL+protext+CTAN+MacTeX is bigger than a dual-layer DVD can hold.  We
exclude a little more from CTAN every year :).

To ameliorate this a bit on the TL side, I thought that a few less-used
platforms could be removed from the DVD (only).  They would still be in
the repository and could still be installed normally over the net (i.e.,
no need for -custom-bin), so I'm hoping no one will mind.

Looking at the list, I propose to prune the following from the DVD:
  mips-irix alpha-linux powerpc-linux i386-kfreebsd amd64-kfreebsd

Any objections (or additions :)?

Thanks,
k