stand/mips: retire BERI boot loader
The folks that created the BERI boot loader no longer need it. They've
long since moved on to other research platforms. Since BERI loader
contains yet another copy of code that I've consolodated; and since it's
impossible to test this platform; and since there are no users, retire
it completely to ease future MFCs.
OK'd by: brooks@
Sponsored by: Netflix
This is a direct commit to stable/13