More code removal, mips ecoff support

[Richard Kenner]

    Woo, end of another era.  Well, you don't see many Irix 4 or Mipsco
    systems around anymore, and the only embedded users will be doing
    r3000s of some flavor, so not much chance for user objections.

Perhaps not much chance of user objects from people *on this list*, but
I think removing support when there are still systems around is a bad idea.
Keeping support for them is not that much work.

Isn't ecoff also used on Alpha?  I have a distinct recollection that it's
the default on the Alpha I use.